I bought my entire system off eBay with 2 exceptions. Psu and gpu. They were both brand new. Cpus are hard to kill, mobo's either work or don't, hdd I had, but the potential for abuse of a psu or gpu is too high a ratio to be worth considering other than possibly a very low end gpu to fit a low end pc where the cards that'll work on that system are really no longer manufactured.
Save up your cash, buy those parts new. Good gpus cost too much to throw away when the item dies 10 minutes after install. Only a DOA will be covered by eBay unless the listing specifies it's a dead item, for parts or repair.