Like webuyanycar.com?
Thinkimg of getting rid of a small convertible I have and never tried any of these types of online services.
Get e-bids from as many online purchasers as possible (using the exact same criteria regarding condition, prior accidents etc) and don't be surprised at the resulting range of offers. I recently sold a 15 year old vehicle this way because I didn't want to deal with strangers and the associated paperwork.
The range of bids was remarkable. Carvana and some others were 50% of what I was offered, sight unseen, by CarMax. I then took my printed offer to an AutoNation dealer and they matched the CarMax offer.
I would also purchase a discount CarFax report to see what accidents, if any, have been reported by the body shops / insurance carriers. The subject vehicle had been hit 3 times in the span of 5 years. I notified my insurance company each time and all damage was repaired by the other driver's insurance. When I printed the report, I was surprised than none of the accidents appeared.
It is one of the questions the e-bidders ask when valuing your vehicle.