I personally have used Garage Kept Motors (GKM) out of Grand Rapids, Michigan. The owners, Jeremy and AJ along with their staff are all true enthusiasts so they are passionate about what they do and in general all things automotive. They also are very honest and upfront so their reputation really helps them sell a lot of cars. So that said yes I recommend them if you live near them, or are looking to buy a car.
I found the experience I had letting someone else sell my car was very positive. There are some costs involved, but bear in mind generally these dealers get a higher price for the cars they sell over private sellers. Most dealers also offer financing so they can typically get a seller in the seat of car much easier then a private seller and using financing option to help a buyer bridge their budget.
The crew from GKM came and picked up the car from my house and trailered it to their showroom. T There they detailed the car, took the photos and videos and promoted the car across multiple venues. That cost roughly $450 upfront, then I paid 15% commission on the sale. They handled getting the car shipped, transfer of title, talking to tire kickers, etc. Literally, the car left and I just waited for the check, no hassles! They did so well on the sale, that even after commission and cost I made out the same, or better if I sold it myself.
I also recently bought through a dealer, Ross Customs out of Goodrich Michigan. Ross also was a big car enthusiast. He loves cars, has a restoration shop, was professional, yet personable and very upfront. Since I paid cash he worked me up a great deal as he owned the car and was not consigning it. So bear in mind some dealers may just buy your car upfront, understand it may be below market as they need to make a profit.
My advice in finding a dealer is check out the reviews online, then talk it over with the dealer about all costs, fees and the consignment rate. It varies from dealer to dealer so shop around. Also ask how they market their cars and where. Finally, do a gut check, after all your research and conversations, do you feel good about it? Does the dealer and have a passion for cars? These dealers are the kind of people that draw other enthusiasts as buyers and sellers. In the case of GKM they have repeat big dollar buyers and collectors who consign amazing cars. My experience is this true of other passionate dealers who are equally successful.
Wayne Carini (Chasing Classic cars TV show, Hagerty columnist, etc.) runs F40 Motorsports.
On the show, you get the impression he does consignments and not just "buy your car and flip it".
Selling a car can be a hassle and the human interactions are not for everyone. So there is value in consigning depending on yourself.
If I lived near Wayne or had a really high-end car I might use him. I don't (lol). But I would be looking for a consignment dealer with a good history in the business. I wouldn't be consigning with someone responding to my online ad with "I can sell that car for you".