Ebay works fine but you have to do your homework on the item and the seller, like you're doing here. With the recent craze prices on quality stuff have gotten silly but a few years back I was grabbing lots of good used kit for cheap.
A few of my best grabs; Bushnell elite 4200 scope $210 new in the box, Surefire millennium weapons light kit $120 complete like new condition, an Armalite scope mount for $25, a FF tube, nut, and grip from an Armalite 10T $12. I've bought a few poor quality chinese parts for my nephews airsoft so it all has its place.
I'll have to admit I spent a ton of time on ebay as a seller myself. I've sold roughly 10,000 antique tools since about 2003. It does take time to sort the wheat from the chaff!