Undervalued sale of older vehicle

I recently had a fairly bad experience selling an older vehicle with low mileage. It’s important to be aware that they need to add 15% on top of the value of your car (as their fee) and an additional 30% on top of that for the dealers they try to sell to. This means they undervalue your car and in my case, a car which sold for 70k to another dealership, they wouldn’t buy for more than 55k with an initial offer of 47k. The agent that came out to appraise the car and the follow-up agents were very professional and kind, but it’s hard to give a good rating for a company which will (and does) undervalue your vehicle to maximise their profits.