Was it misrepresented? Return it - penalize misleading practices.
Was it junk? Return it - penalize hiding that something is junk. (is it priced like junk and not shy about it? great! you know what you're getting! junk can be useful!)
Was it just a bad fit for you and nothing is wrong with it and it might work for someone else[1]? Return it - encourage more thorough descriptions. E.g. "one size fits all" is an extremely lazy lie that just cost you money, measure it and tell me the measurements - they are perfectly capable of that and almost certainly did it multiple times already while creating the thing. (though for some I do feel bad about the cost it imposes, and don't always return here. depends on the details.)
It's not a 100% "I just don't want it" thing, there's plenty of regret-purchases that I just hang onto and give to someone else or sell at a rummage sale. But I definitely don't feel bad about using returns as a "stop being hostile towards your customers" tool.
It's also roughly the only way consumers as a whole can provide feedback to a seller that won't be ignored. Communicate your opinion clearly.
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[1]: Headphones are a pretty good example here. They like to claim sky-high perfection and durability and features, and then ship buggy crap with no support or wildly misrepresent sound quality (e.g. frequency response is quantitatively measurable so measure it, leaving it up to niche reviewers is worse for everyone). Lots of luxury-adjacent products do stuff like this, and I do not feel the least bit bad about calling them out on it - this stuff gets measured during development, used to select materials and tune the final product, and then hidden from you to sell it. And then they often change it after the initial launch, and do not tell anyone. It's blatant hostility, and it deserves to be treated as such.
Especially if it's a small business, I can practically guarantee the business owner is hoping beyond hope that if there's an issue, you feel willing and able to mention it and get a return. You bringing it up makes the business owner aware there's an issue, and at that point they can do everything in their power to make it right with you, because chances are they're kept up at night worrying about all the ways to make their customers satisfied. If someone sent back food at the shop, my first though was "oh my god thank you for mentioning there was an issue." The potential loss of money, the extra time and trouble, all of it is pennies compared to the stress you feel when you wake up at 2am and realize holy fuck you forgot to add the extra bacon that one customer ordered. I imagine it's similar if you find out, idk, after shipping out 50 units of something, that the way you're boxing it is causing units to show up just a little bit banged up or whatever. Much better to know right away and make it right with people!
So, I'm not sure if this is you, but if you're being held back by some sense of not wanting to cause trouble, trust me, you're doing the business owner a huge favor letting them know.
Still some kind of sense of personal responsibility for the decisions I made changed for me in the last five years. I still don't buy 5 pairs of shoes and return 4 or anything like that, but maybe that's more out of laziness.
(For example, in my cart is a few different ~$100 sandals of one brand. I've hesitated to purchase one, since I don't know whether I can risk a 9 non-wide in my preferred style&color. I won't be able to tell whether it fits me well enough until I wear it outside awhile, at which point it's obviously been used on someone's foot, so I'm not going to return it.)
(I also contort my Amazon and Walmart orders, to try to keep them from shipping together items that I know are likely to get damaged that way.)
Yet, the rate of defective and damaged items that arrive from online purchases is high enough, that I've gotten past much of the discomfort for those returns.
(For example, this week, I returned some supposedly brand-name diningware, which the brand's customer service themselves suggested was counterfeit because they simply don't sell it in that branded retail packaging. I'd contacted the brand because the product didn't look quite like the previous one I bought of that brand, in a toxically-tainted-materials kind of way. Guilt-free, annoyed return.)
So I figured I have a normal level of return, as a result of returning obviously defective/damaged items... until I saw this article claim the online return rate is "almost 30 percent".
If I had a retail business with someone doing 30% returns (outside some program for trying on clothing at home for sizing), I would want to fire that customer.
(And for the official clothing try-on-for-sizing program, I't try to throw innovations at that, to get the returns down.)
And furthermore now that I'm doing so many returns, I've become completely fine with returning new unopened things that I decide I don't want, effectively delaying the actual purchase decision 30-90 days. Parts that I want to have on hand while doing a project, limited time deals from pricing games, extra copies I order preemptively to quicken the above self-QC song and dance, etc. If I already have to go to a store to drop off returns, my marginal cost of returning additional things is very low.
If returns were really affecting bottom lines, companies could do a lot to tamp down on these dynamics. At this point I suspect it's more profitable for them not to. I think the manufacturing costs of stuff has just gotten so low that the physical items themselves just don't end up mattering compared to the overall margins.
However - I have been a Costco member for 25+ years - today, for the first time ever, I returned something far after the original purchase. In January 2021, I bought a 2-pack of CO2/Smoke alarms from a major brand at Costco - they were supposed to have a 10-year internal battery. Well, both of them failed about 2-months ago - constant low-battery chirp, no amount of executing the "test function" would fix them.
Costco, being the absolute best "retail" corporation on the planet took them back and refunded the original purchase price - the service staff laughed as the chirping started driving them nuts when they accepted the items. We did our normal shopping, and as we were leaving - chirp, chirp, etc...
In my view, anything advertised doesn't work, arrives broken through negligence, or misrepresents their specifications is going right back to where it came from.
But, brick & mortar stores rarely have clothes that fit me* AND I somehow end up between sizes, so I tend to order two of everything (in S and M, or whatever) and return the one that fits worst.
From an environmental standpoint, I have no idea if this is better or worse than having fully-stocked brick & mortar shops. But, fact is, those don't exist any more, so this is what I do.
* At 5'7", I'm slightly on the short side for an American male, and at 150lbs, I'm smaller build than most as well. IME, clothes are either cut for skinny teenagers or for dads with 38" waists. And I'm neither, leaving to try on and return many items.
Edit - since maketheman's post got killed... I've yet to find a clothing brand that lists thigh or arm diameter, which tend to be the problem. The "slim-fit" stuff you mention usually fits my waist or torso, but will not go over my bicep or quad. And the normal cut from the same brand fits like a trash bag. I'm fine getting tailored clothes for suits and suchlike, but I'm talking about jeans and casual shirts here. Anyway, it's a totally first-world problem to have, I can deal with it.
2) You're gonna want measurements of your own actual chest, neck, and natural waist. Easy to DIY close enough for this, no need for help.
3) Also, measurements of some clothes that fit you well. Shoulder, seam-to-seam; arm length; pit-to-pit width.
4) The brands from #1 will have charts that provide measurements for their clothes, or else suggested body measurements at a given size. Use the info from 2 & 3 to get good guesses at which sizes and fit variants will work.
5) Thrift or ebay some options. You can resell the ones that don't work out for close to what you bought them for, if it's worth it to you, or just dump them at goodwill. You're paying a few tens or a little over a hundred dollars in failures to find your sizing in a few brands. This is basically the only totally-lost cost to this process (and again, you can actually recover most of this if it's worth it to you)
6) Now you know your size in a few good consistent-sized brands. Ebay with your exact size in each brand (use saved searches, like "(jcrew,j.crew,j crew) 'extra slim' medium shirt") or sale-shop directly from the brands' sites. No, or very few, returns needed. You can also thrift-shop much more efficiently, at least at places that size-sort. You're just skimming for brand tags you recognize, and totally ignoring everything else.
[EDIT] And actually with the measurements from #3 you can ebay lots of shirts from brands you've never tried, with reasonable success rates—any listing worth bothering with will provide pit-to-pit and (when relevant) sleeve measurements, at least.
What's missing from the regular usage of the term is the fact the pamphlet was written immediately the enclosure movement had subdivided the literal Commons - common land - that had functioned perfectly fine for centuries without over exploitation... until the enclosure movement subdivided them and landowners began over-exploiting them.
The lesson isn't that people can't be entrusted with unfettered access to common goods, it's that giving decision making power over the distribution of a common good to an owner (capitalist) will result in over-exploitation. In the case of returns, the price of the good has way more to do with the seller just getting the price up as high as they can get it and still profit, and far less to do with labor costs, manufacturing costs, shipping costs etc. A simple question: if they could sell it for more and make more money, why wouldn't they? If they could sell it for less and make less money, why would they? Hence why the cost of goods stayed up after the chip crisis despite the chip crisis ending.