I am both a car wash owner and a long term licensed real estate broker. As a real estate broker, I have experience with residential, commercial, and "business opportunity." What the OP wants to sell is both real estate and "business opportunity." Some real estate agents and brokers have experience in this area, but many do not.
First: I would decide if I am going to try to sell it myself, or work with a broker. A car wash is one of the most difficult things to sell yourself, as it includes land, fixtures and equipment, and business opportunity (i.e. on-going business with revenue and expenses.) There are almost no guides on valuation or how to proceed, although Pat Crowe years ago wrote the "Car Wash Appraisal Handbook" which at least was a start.
The "pros" for selling it yourself is you will save a commission on sale, usually 10% but maybe less. Commissions ARE negotiable!
The "cons" for selling it yourself is it is a great deal of work, you will have limited market exposure to buyers as you cannot insert it into an MLS system, there is a risk that you will screw up your numbers and presentation, and you might get sued for acts you do, including acts of "omission." Which means you get sued for not doing something you should have done-- even if you didn't know you should have done it. Finally, calculating your "net profit" to present to a future buyer is more complex than most realize-- it is a calculation to computer "SDE" (seller discretionary earnings) and it is more complex than what you put on your tax return. (You need to back out things like property tax, and more, which serve to increase the computation of SDE to a number higher than your net profit.)
What I would do is this:
1- Do some basic research on real estate firms in your area. See which ones handle sales of business (not just houses.)
2- Contact the BROKER of these firms directly (not an agent working for the broker.) Tell the broker what you want to do, and ask what their process is if you want to work with them. It is OK if the Broker wants to assign an agent to work with you, and that is typical. But start your first contact with the Broker.
3- Get at least 3 real estate firms to make a proposal to you about how to market your business. They should describe their
marketing plan for the business, which includes signage, print media and flyers, and so on. The better the
marketing plan, the more interested I would be.
4- You can also consider a national firm, like carwashbrokers.com. I have never dealt with one of these, so I cannot comment either pro or con.
After you do the above steps, decide if you want to: a) market and sell it yourself, b) choose on of the real estate firms to do it, or, c) expand your search and interview more real estate firms.
Important point: Most of your "thunder" of interest, excitement, and attracting a new buyer happens within the first 30 days of exposure to the market. What I would not do is merely post a "Business For Sale" sign at the business to "see what happens." If you do that, you greatly dilute the "thunder" you or others have if you choose another route later.
Hope that helps.