1. Cars with Loans on them. This actually is a hassle, especially in states where the loan holder owns the title. You literally can't just sign the title over to them. In most cases, the buyer has to pay for the car, the seller uses that payment to pay off the loan and then they get the title to transfer over. There has to be a ton of trust there. Even with a bill of sale, everyone is afraid of getting screwed. 2. The straight craigslist process is not quite that easy, respond to emails, some of them from people not even really interested in the car. You have to go back and forth scheduling viewing and test drives. Roughly 40% of the time, you have to drive out to meet someone. If they no-show? Or low ball you? Or don't want it? Time is wasted at all of these steps. 3. Some people hate negotiating, and don't know what a fair price is. We help. 4. In Cali at least, you need Reg 262 for vehicle transfers. It's a form you can only get directly from the DMV (can't print it online). I went to the SF DMV the other day to pick some up, the line was over 2 hours, just to get a form. Needless to say, I put it off for another day.
I agree, for some people it makes the most sense to just sell it themselves. But it's not always a straight shot.