I have been doing yard sales, etc. for about 30 years now. Not as much anymore, at one time it was a serious sideline of mine and I made very, very good money doing it. Of course, pre internet days were the very best chance for the educated buyers to score on the un educated sellers.
The world of business is, and always has been buyer beware, and seller be educated- PERIOD! I have bought $500 worth of billiard stuff for as little as $20 on many, many occasions. Cues, cases, billiard room chairs, cue wall racks, all sorts of vintage billiard items- you name it.
I bought many, many categories of items, from watches, to golf equipment, cameras, musical instruments, etc. etc. - I educated myself on every collectible category that I came across in the past 30 years- sometimes I took a flyer and struck out as well- only to go back and reeducate myself about a particular collecting category.
Most of what I bought over 30 years has been sold at a profit- many were huge profit percentages- like a 50 cent 1930s Hamilton Stanley watch ( Illinois watch co. movement) ---that I sold for $500--- some items I have to this day- including two of the most highly desired Meucci cues ----- bought for $20---unfortunately, death and divorce often led to these items being available by sellers who were either uneducated about value or simply wanted items out of the house, or needed cash.
Most of this has changed with the internet, and the pure numbers of folks who go on the "hunt" - at one time it was a very small closed community of " pickers" - no longer- shows like Antiques Roadshow busted open the whole secret world once inhabited by only the slyest of buyers- I was one of them, and I loved the hunt and the FIND, as well as the resulting CASH.
I never felt an ounce of guilt about a purchase or a sale- because I never lied, cheated, or stole--- I gave what was asked and I sold at an offered price- that is the business world plain and simple. I made it MY business to KNOW- to educate myself on ALL things sellable.