Avoid Arctic Cat(Textron), Polaris and Canned Ham like the plague. Honda, Yamaha Suzuki and Kawasaki's are far more reliable. Stick your finger in the exhaust and feel for any oily residue. On cold start up, watch for the blue puff of smoke or white exhaust. Blue can be worn rings and valve guides. White can be burning rad fluid. Dinged up plastic parts can point to abuse although minor scratches, etc are fair game. Dings and dents in the rims can point to "hold my beer and watch this" type of use. Oversize tires often lead to wrecked bearings, ball joints and tie rod ends. Snorkels are another dead giveaway to playing submarine in the swamps.