craiglist is free, but only for local
I have run into some real wackos there too. Bottom line buyer beware, it's just the way it is..
In 2005 there was a father & son scope repair & resale business on ebay. Great feedback. One day the son decides to sell a $500 scope he does not have, and I bought it. Ebay closed the account and that's as far as they would go. I eventually got my money back from the father, but it took a lot of work and a great deal of luck on my part, and honesty on the father's part to make it happen.