I've bought various bits of Amiga stuff from Ebay, my best deal was a PPC card for my A1200, at the time they were going for around £250 on ebay, but I got a dead one for £80 and fixed it for 20 pence (needed a new capacitor soldering on to replace one that the previous owner had accidently knocked off :-) )
I don't think I have every sold any amiga stuff, I tend to keep hold of stuff like that. I did try to sell the AmiGBG DVD on ebay but got exactly 0 sales !)