Ebay
I have bought and sold radio's on ebay. As for as illegal when the seller post it as wide band consider I have sold radios as far away as India to remote locations where people have limited US $$ and noone else to fly with. Some have bought the radios and converted to freq legal in their country which might have never been legal in US. So consider that ebay is world wide sales and not just for US.
I also have just + feedback but would accept back anything I have sold had there been a complaint. What I have found is that most modelers are upfront and honest. If buying used I would ask "If I take it out of the box you send it in and take it to fly immediately will it work?" Get a yes / no answer.
I have bought radios that were listed as working.. and when I got them they needed over $100 to make them flyable. Working, might mean only turn on and not capable of flying. So be direct in asking a question.
When I sell equipment I have flown I will state so in the add. If I have not flown it I will also so state. However I also assume no responsibility after the sale for a crash. Just many points to consider.
have a nice day.