Stuff happens like that. I got rid of a bunch of books for $75 and then remembered I had left an envelope with $75 in one of the books. C’est la vie.
And yes, I have found amber and pearls and amethyst in silver in thrift shops for fifty cents or a buck and an original 1920s book full of Maxfield Parrish illustrations for a quarter and an antique brass bed for $25, or a purse with even more interesting art deco items overlooked inside, among other things. During thrift treasure trolling, one looks for fallibility of the appraiser, betting one’s eye is better than theirs.
Yard sales can be even more interesting, especially in the better neighborhoods. Sometimes things of extreme value are sold for peanuts because the owner does not want to be reminded of the giver.