Sadly you can't sell your business on GTAO, You can trade them in for better ones or you can do what the following reddit post states:
MC Businesses are a more passive system compared to CEO work. However, they have a high upkeep cost, and if you own all 5 Businesses and have all 5 running at once, you'll be charged 30 grand every 48 minutes. This is the down side to running these criminal enterprises.
However, if you go to the Admin Laptops after a sale and shut down the business, the upkeep costs will drop. Your employees will leave, but any unprocessed supply will stay stored, and all upgrades will remain. Just make sure you sell off your finished Product before you shut down, or else you will lose it.
Essentially your business goes into hibernation once you shut it down. Upkeep costs drop also. Essentially you'll just have to pay the much lower property tax when they're not running, which is just a few thousand.
Shutting down is ideal to do after a sale, because it will help keep your daily taxes down. Also you'll only be producing when you want to be, rather than say, keep the meter running, as it were.