Yard sales have only been going for about the last month here - gotta wait til the snow goes, ya know!

We've gone to several each Saturday so have gotten a few bargains this year. DH got a set of router blades in a wooden box, some had never been used, for $10. I don't bargain much anymore, just pay what they ask if it's something I want and the price is more or less right. He also bought a boat last year for $40, fixed it up, and plans to sell it for at least $150.
Over the years I've found lots of new stuff, still in the package. Have been amazed at what people buy (or perhaps gifted) then don't use and sell for pennies.
Used to sell "pre-owned treasures" so can't remember everything I've bought and sold. I used to love buying something for $2 or so and selling it for $15 after cleaning it. Often people just want to get rid of things at YS's so price really low. You have to be careful what to buy for resale tho.
Probably the best bargain I bot was a hand blown art glass rooster for $5 which is more than $100 retail. Have bought lots of things for 25¢ which I knew retailed for at least $10 and things that I paid $2 for which were $60.
I think many people don't realize that many items in yard sales are just like new when washed. I have no reservations about using "pre-owned" items from YS's that can be cleaned. Unfortunately around here antiques are few and far between. I did get a nice tea cart for $40.
I was really pleased with the free drapery and upholstery fabric samples I got last year - some are quite large pieces and great for crafts and sewing projects. All have successfully gone thru the washer which also means when I make cushion covers or whatever out of them they won't shrink more.
My best bargains are the things I collect that I like such as oil paintings from $1-$20. Also silver holloware for which I have never paid more than $5. each even for large trays and really nice pieces. Also have found quite a few pieces of quality handcrafted pottery very inexpensively. Just bot one on the weekend for $2 which retails for $20 and I know this because it was probably something I sold new in my store.
Of course something is only a bargain if you like it or can use it.