The 400D is OK, it has a cheap plastic body so dont knock it around to much. As a rule I dont buy anything secondhand when it comes to cameras because you dont know what they have been through! So if its cheap thats fine but dont expect to much, then if it works good then thats great!!! Always ask why they are selling it, obviously test it before you buy, problem is you cant see many faults on the small screen. generally Canon cameras are great, thats all I buy! Also watch out for the cheap lens kits they offer, generally they are ok for happy snaps but are substandard for anything else! Canon Ultrasonic lenses are good and L series are better (but expensive). It all comes down to what you pay is what you get!
What lens comes with it? for V8 supercars you would at least need a 200+mm lens to get a closeish shot (100-300mm would be good).