I have only tried to sell them stuff once.
I sent them a Minolta lens and a Vivitar 285 flash.
They would not take the lens but gave me an amazing offer on the flash, way more than I thought it was worth.
Funny thing is I sent the flash with the all the original box, instructions wide angle panel etc and they sent all that back?
That's weird, especially considering they do sell instruction books and accessories. I think they miss a chance to make a little more by not selling mint condition stuff with boxes and cards if they came with them.