I hate selling cars. It's troublesome and time consuming, so you I'd gladly pay for the service. The pricing turns me off though. Selling a 50K car, the commission would turn out to 2.5K. That's net. So with 50% income tax rate, I'd have to earn 5K to pay the commission.

That's much too steep for me. If there was a cap of say 1K, I'd be a customer in a heartbeat. But 5K gross is certainly worth the inconvenience of selling it myself.