EBAY: if seller 'offers returns' - it is safe and smooth, more time consuming and several careful steps to follow to return something not as advertised...I bought from a scammer but eventually got refunded, including shipping charges.
I've taken a beating on selling some things on ebay auctions when I was impatient to sell something.
Some of the current sophisticated scams on ebay now limit my purchases there to items less than $200. I have a low risk tolerance.
Fredmiranda: I've bought several excellent items, but paid KEH prices. Some well off folks on there who buy everything new, play with them for a while and then sell them on.
KEH and Adorama: I've had good luck with both, but no bargains
Craigslist and OfferUP: Too much work any more for me to sift through the crazy high prices on most photographic things, a good bargain will pop up every month or two. The owners clearly do not check the going prices on ebay before advertising their items.
The pawn shops are clogging up the listings with some real junk and I've had a couple of sellers not show for the sale and then go silent. I did buy a D100 / Tamron 90mm macro combo along with a big box of other Nikon goodies for $30 on there last year. I've averaged two purchases per year for the last 8 years on the CL/OU sites.