CPO means it went through a 172 point inspection. If anything doesn't pass it gets fixed, otherwise they won't Certify the vehicle.
By making it a CPO, a Chevy factory trained tech stands behind the mechanical condition of the vehicle. You get the balance of a 4 year/48,000 mile bumper to bumper and a 6 year/100,000 mile power train warranty. Rental or not, the car has checked out.
Price inline with KBB Fair price for CPO car
Factory certified with tons of warranty left
I wouldn't worry about personal car vs rental car.
I sold my 2016 1ss for $27,500. I did 100 drag strip passes and 4 or 5 autox days. I was honest and told my buyer all this. If you buy private party, you might get the honest story. If you buy a personal vehicle that was traded in to the dealership, you get some history on the vehicle, if you managed to run into the salesman that took it in on trade. You don't know what has been done to a rental but do you think the rental car you're looking at has been down the strip 100 times?
If its in good shape, has good warranty, is a good price, BUY IT!