Why would Cargurus rate my sale as being a terrible deal while comparables are rated as great deals at a higher price? Is Cargurus requiring upgrading my account to get a better rating?

Rating would have nothing to do with your account. 170,000 plus miles might or it might be a glitch in the system. Contact CarGurus for help as this forum is for car questions and it is not frequently monitored by CarGurus' staff.

Private sales are rated cheaper on all the car valuation sites I have seen. If you are trying to get a dealer retail price for your car it would probably indicate a high price.