If yoú're not racing then buy used!!you can get one like a year old and save a few grand, just wait to find one that hasn't been abused and you'll be fine. and if you're getting one like 5 years old then ya just make sure it's in good shape.
personally i wouldn't buy a used race dirt bike, usually their maintenance is up to date but the thing has still been ridden the crap outta it. Just wait and find a quad that the guy used on his property or trails or something, then you can almost garantee it hasn't been ridden hard.