there are items on ebay, and there are items on ebay
some are completely dodgy items :
scams, electronic superchargers for 75HP which are a fan in the intake pipe on an n/a car
those 5HP resistors etc
600HP turbos for $600
not hks apexi nismo greddy tomei ashtray
dodgy traders
then there are good bargains well well know traders and shop "runners"
usually have really high feedback and sell good stuff just cheap
without the added bullcrap of running a normal retail store
choose carefully but remember there are lots of bargains
just be careful, double check, ask, lots of reading and check their feedback