I buy stuff on eBay and mostly have been happy with it.

You do need to read the ads carefully to be sure you're seeing the actually item for sale. eBay sellers are like any other small business people. Most are honest, but some aren't.

I've not sold much, but recently put a car on eBay that had not sold locally. I still had it advertised locally and said so in my listing, reserving the right to end the auction if it sold. I quickly had bids approaching what I hoped to get. And then they went higher.

Meanwhile several local guys inquired about buying it 'offline' since it was for sale locally. One of them was serious enough to offer more than the highest bid.

He came and got it. I happily paid for the eBay listing, since that was where the sale really came from.

I really enjoy swap meets as an activity, but don't seem to buy much at them. The one time I bought a space I sold exactly enough stuff to pay for my space. It had cost me more in gas to get there and back... I probably won't repeat that experience.