I have two good answers - both involving a rare brand of watches (Patek Philippe). One in a thrift store one in a pawn shop. I should mention for those who do not know that Patek Philippe are THE high end watches. In addition to their normal work they make one off custom pieces for people. I mean watches that NEW may be $200,000. But you can find plenty in the $500 to $25,000 range.
I collect pocket watches and have done so for about 30 years. I used to have a job that required travel all over the country, so I used to haunt pawn shops and other likely places looking for good deals. Mostly from pawn shops. My wife and I were not the “pay high price for special pieces” kind of collectors but the “Look what I found for $200!” kind of collectors.
I even had a good “patter” down. I would call all the pawn shops in the phone book - not the high end ones with a lot of jewelry, because they would know what they had, but the ones with a lot of power tools, guitars, and SOME jewelry. Those were where you could find something good. So I would call and say “Hey - my dad is just about to retire and I want to get him a gold or silver watch, but I want it to be a really old one. Do you have any…like pocket watches?”. So they did not think of me as a collector. Worked pretty well.
so - I was walking down a street in Boston in maybe 1990 and spotted a few pocket watches in the window of a thrift store next to a very old church. I went in to check the out and two were junk, one was a Patek Philippe gold pocket watch from the 1920s n decent shape. Worth maybe $80,000. In 1990. Price was $200.
I took it up to the counter and was facing a sign saying “All proceeds go to support our school. All staff are volunteers.”.
Well…crap. So I told the woman what the watch was worth, and that there was no way I could buy it but they should take it to a reputable dealer of rare watches and sell it. If it had been a pawn shop I absolutely would have purchased it, because it is their business to but and sell and know what they have. But a charity thrift store. crap.

A few years later I was in Atlanta. Call a few pawn shops. Call one and did my usual routine. The guy who answered had a pretty thick southern accent.
“Yup. Got a few old watches. Let’s see. Got a Waall-them (waltham) in a silver case. Kind of dinged up. That one is $100. Got a eel-gin (elgin) in a gold case. I think that one is pruty old. Thats $250. And let’s see. Hmm. Got a “Patak pheel-eep-A”. Huh. Patak Pheel-eep-e? Yup. Thats what it says. Must be a foreign watch. Thats in a real nice silver case.
me: “Uhh. that sounds good. how much is that one?”
Him: “well, that watch is $35,000 son! You thought you had me didn’t you?”
me:” Yup. Can I come down and look at that? I can’t buy it?”
Him (suddenly with no accent): “sure, but we are going to laugh at you when you get here”

So - I guess that second one was not a stunning find…but I thought it was for a minute!
The first watch was a lot like this one. but had an alarm/chime with five tones. very rare.