All great advice.
Used XRAYs probably are, on average, a safer buy than most other brands, but I have met many guys, both onroad and offroad, who I would never buy anything from, unless it was still in it's factory sealed packaging.
The only used cars I've ever bought were barely used and were from racers I know personally. Guys who really know how to build and maintain their cars and the deals were just far too good to pass up. I also knew exactly why they were selling their cars and it had nothing to do with the cars.