Margins on the products range from 60% to 90%+, so optimization on the 3~5% that Stripe accounts for is not super-meaningful to my business. (For completeness: also use Paypal, at their 2.9% tier. Have never been dissatisfied with what I pay for CC processing.)
For a $100 sale that costs $75 (a 25% gross margin, typical for internet sales), and a payment fee of 5%, the fee is $5, or 20% of the $25 gross margin. Each 1% of fees represents 4% of gross margin. That fee will represent a much higher percentage of net profit, after deducting other business costs.
This effect increases dramatically as gross margin decreases. At 20% gross margin, 5% represents 25% of margin.
For a low margin business, say 10% gross margin, a 5% fee represents 50% of the $10 margin on a $100 sale. If other business costs average $3 on that sale, the payment fee takes out $5 from the $7 margin, or 71%. A 1% decrease in payment fees increases net profit by 50%, from $2 to $3 on that sale.
So you can see on low margin business, payment fees have an enormous effect on margins and profitability.
Credit card processing fees are somewhere around 2% - 3%, so in a marketplace with all credit card transactions, impact on margin will be 6% - 30%.
If that marketplace can implement alternative payments (e.g. ACH, bitcoin, etc), impact on margin can get down below 5%. Not sure how the ebay / paypal integration influences this - would be interesting data.
One additional method to reduce margin for marketplaces is to allow transactions to occur offline and then invoice the seller based on a % of the total amount. Then your impact on margin will be exactly what your processing fees are.
There will be much different dynamics for different revenue models (e.g. as patio11 said, in SaaS, it is basically irrelevant).
So, I argue that % impact on margin is not a very useful metric unless you are comparing a specific revenue model in a narrow vertical.
Would you rather have $10B of margin with 50% going to processing fees or $1M of margin with 0% going to processing fees?
2-3% is incorrect - it's 2-3% + $.30 a transaction. Keep that in mind - for anything under $30 the $.30 is a bigger deal than the 2-3%, anything over $200 the $.30 has largely ceased to matter and the % is what is relevant.
You can't take Square online and only pay 2.75% - if you could though, that'd be amazing!
I'd like it to be lower, but on the other hand, a few additional sales due to confidence in PayPal probably makes it an overall gain for me.
So, like others have mentioned, I'm paying a standard PayPal rake of ~3%, but don't really feel it because the product has been profitable for years and doesn't have any real variable cost.