When shopping for bass boats, look on the side for the word "Ranger" and if it has that and the motor has "YAMAHA" written on the side, you're good to go.
(I couldn't pass up that opportunity.)
Really though, Champions have a rep as a good big water boat. Do as Jon suggests and go ask the guys at BBC and it'll be like swatting flies all the responses coming in.
Check the motor-compression, bleed down, shaft run out, pressure check lower unit, etc. Check the transom on the boat by stepping on the lower unit, and making sure nothing moves or flexes in the transom. I could go on and on about stuff to look for, but I'll stop here and just say look the boat over as if you were giving it to your mom. If the wiring looks like crap, and like it's been redone by someone that just didn't give a crap, then it probably has been. If the steering is leaking and looks like it hasn't been taken care of, then it probably hasn't been. That sort of thing.
And test drive it. Make sure the motor is cold, and has sat cold for a few hours before you go to start it. Then run it, accelerate, idle, WOT, shut it down, start it back up, and do it again. If the seller has a good boat, he'll be more than happy to take you out and let you drive it all you want to. If he balks....may not be a bad boat, but it's a red flag.
Champions are cool boats. If I wasn't in a Ranger I'd be in a BayCat or a Champion of some sort.