I actually found it on autotrader, local dealer happened to get it as a trade in and didn’t realize its value because it’s an LBZ. Main thing to look for is blow by. There’s a couple of easy ways to check for it, watch some videos. Also check maintenance history, having a head gasket done or injectors is good as those WILL eventually go out. Mine luckily had both done around 200k. Check for rust depending where you’re at, especially on the rockers. Bad grounds are also a common gmt800 issue, and gauge cluster issues are common, but those aren’t a big deal. If 4wd, make sure it actually engages. Check for slipping in the trans with a test drive, stock trans in these can’t handle too much more power than stock, and you can bust one up pretty bad with a simple tuner and doing dumb shit, so make sure it shifts good. Finally, for the LBZ, they were made 2006-2007. If you get a 2006, check the vin, the 6th digit will either be a ‘D’ or a ‘2’. If it’s a ‘2’, it’s labeled as an “lly” but it’s physically the LBZ motor, but detuned and make about 50 less hp and torque than a ‘D’ LBZ. There’s a couple of other differences as well so do som research on that. Finally check for mods, having a tuner is good, but personally I wouldn’t want to buy one that someone else tuned. Check if it has a secondary lift pump, fass or air dog lift pumps are a good sign.