Hey I wouldn't buy refurbished amps off eBay. It'll cost you more than a new one if it breaks down. Try your local shops for refurbs. However, new amps are a different story. I have bought new amps and so far they're great.
I bought a Rockford Fosgate Amp off of Ebay. It was to power 2 Lighting audio 12" subs, the subs asked for 250W RMS. The Amp was rated 300W RMS 900W max. The subs sound friggin awsome. Amp never broke down on me, always ran strong. I never got it tested to see the numbers though. Ownd it since May. Selling it now, want a sweet RF amp?
I know I might be slammed for this, but I bought a refurb. sony amp off e-bay about a year ago, I listen to my music pretty loud sometimes, and I've never had one problem with it, infact, I have a whole sony system, and haven't had any problems.