That's what I hope to do : Just find something I like, and when I look it up, find out it's worth more than I paid.
This is how to do it, and it's the big difference in collecting world coins compared to U.S. coins. People can hope to cherrypick some rare variety from a bin of 500 Mercury dimes, but you can go in a dealer's foreign junk bin and pull out 100 undervalued coins in one visit. It's what I live for when it comes to coin collecting and almost the only way I care to buy anymore.
The thing about this that strikes me as weird is that each coin in the bucket was in a small plastic medicine bag. Not sure why, but he took the time to put every single coin in its own small bag. That means he had to at least have looked at the thing or had enough time to think over whether it was worth putting in.
Yeah, how could he not spot a large silver coin? Maybe he thought it was copper-nickel. As they say, "Don't look a gift horse in the mouth.".