Prices are insane right now. $23K is a good price. Check for rust on the rear quarter panels all around the wheel wells and along the seam between the quarter panel and the plastic bumper/fascia. Also check for rust on the lower rear quarters between the rear door and the wheel well. Any signs of paint bubbling is not good. I would also check for rust on the lower inside seams of all the doors (where the outer panel crimps over the inner panel) and the inside front seam of the hood. Common areas of rust, especially for a WI vehicle.
Re prices, I'm seeing prices for 2016/2017 Tahoe's with 40K miles that are similar to what I could have bought one new for back in the day......