If you had bought this picture for $2 later to find out it's worth $5,000,000, would you feel an obligation to share some of the proceeds with the shop from which it was purchased?
Lottery tickets are not a parallel, given that it's luck of the draw that determines the value of the ticket. At the time of purchase, the ticket is worth exactly the price of the paper it's printed on.
Here's a better, less extreme but real example. I just purchased a mandolin from a seller of vintage guitars. Paid $750, and were I to be patient I could probably get $1200 out of it. I have no plans to sell it, as I bought it to play, but let's supposed six months down the road I do sell it. Do I send a spiff back to Jimmy's Vintage Guitars? Nope. Jimmy admittedly doesn't know jack about mandolins. Jimmy didn't even get the model right, even though sixty seconds on Google would tell you the one easily-seen distinguishing feature that says it's a Gibson A-50 and not an A-40. I don't feel bad for Jimmy, because if he's going to take stuff to sell, he should know what he's selling because it's his business. Jimmy better have a big pile of "Vintage Instruments Value" books on the shelf, and know how to use the internet. I also assume that whether he obtained by trade or cash, he felt he got an acceptable deal when he took the instrument. So even though I got a bargain, Jimmy came out okay, too.
Now, I'm not a total bastard. Were I to find, say, a 1923 Gibson F5 at a yard sale for $50, I'd give the person $500. Two reasons for that: such an instrument is worth several thousand dollars even in rough shape, and I don't expect a person selling Grandpa's mandolin at a yard sale to have any idea of its value. They're not in the vintage instrument business, they shouldn't be punished (too much) for not knowing what they're selling. They get 10x what they were asking, and I still get a steal, everyone goes home very happy.
In the end, someone got lucky and it wasn't the person that sold the picture. I might very well kick back a little to the original seller, but I most certainly wouldn't feel obligated to do so.
Tipping dealers in UK casinos is actually forbidden by the 'Gaming Board' (gambling commission) to discourage "cheating" since they believe that if dealers might get a cut of the winnings they might be inclined to stack the odds in the player's favor.
Are you sure about this? I've played poker in UK casinos where tipping was very common
"Licence condition 10.1.1 Tipping – personal licence holders All non-remote casino operating licences 1 Licensees must only permit tipping of staff holding personal licences where a tronc system is operated; that is to say, where all tips are pooled and distributed amongst the employees concerned. A separate tronc may be operated for each of a number of categories of licensed staff."
http://www.gamblingcommission.gov.uk/pdf/Latest-LCCP-and-Ext...
http://www.hmrc.gov.uk/manuals/nimmanual/nim02941.htm
Edit:
It's seems that all tipping was universally disallowed until 2005 (haven't been in a UK casino for about 10 years)
"In the rest of the world, tipping the dealer for success is the norm. In Britain it has become legal (on implementation of the 2005 Gaming Act) and now it is acceptable. It is still however not as commonplace as in other places in Europe or America."
Beyond that it's subject to the 2005 gaming act and the tornc and personal license holders schemes.
Sourse: German in a rural and traditional area
But I understand why this idea comes up. Put yourself in the shoes of the "junk shop" (from article) owner or flea market vendor. We're not talking about a high-end antique store. The seller is likely not wealthy. They're going to be devastated that they let this opportunity slip through their fingers.
A tip or kickback of, say, $25,000 would only be 0.5% of your pre-tax gains, but it would likely be a significant windfall for them, let them pay off some debt or take that vacation they've always wanted to. It's a nice gesture and would help take the edge off that anger and regret they'll inevitably feel for the rest of their life.
However, before I did that, I would consult a lawyer. On the one hand, sharing a small piece of the pie with them might give them something to lose and make it less likely they'd bring a frivolous but possibly expensive-for-you lawsuit against you – by an attorney who's working on commission and betting that you'll settle. On the other hand, giving them a cut might open the door for some line of reasoning or set some precedent that they're legally entitled to a portion of the proceeds. I don't know. That's why I'd consult a lawyer. :)
I'm not suggesting any sort of obligation towards the junk shop; it's an interesting thought exercise of where one draws the line when there's a knowledge gap between buyer and seller, particularly one involving six orders of magnitude difference in value.
1. oh that picture looks nice, i'll buy it, and then have it appraised thinking it might be worth a couple hundred bucks
2. Is that billy the kid? this could be really valuable, let me see if i can get it for a song