if you're looking for a standard def camera, this is the way to go. 300 hours is pretty high. I don't know where you live, but you can often find DVX100a or b on craigslist for around that price, maybe a bit higher, and many of them have almost no hours (below 50). It's meant to live past 1000 hours, but just the fact that his camera has 300 hours on it means that it's been used alot, and may have seen some wear and tear. If the camera is in good physical condition, as well as 100% working condition, go for it.
PS, if you buy it, buy a cheap MiniDV camera (if you don't already have one) and use it to upload your footage. It's better for the camera heads to not replay lots of footage, and it also keeps the hours low.