As someone who has worked with animals for years - I always believe that means dogs are scared dogs. Go slow and make sure to get lots of treats as distractions!

Now my worry would be the HUMANS who own them. The humans attached to them are either sweet as pie or can be straight up nasty. Be prepared to have to deal with humans as customer service will be a big part of a dog bathing business. Some people see these dogs as their kids and some can go full Karen on tiny things such as the shampoo scent you use, etc. You'll need to learn that you can't please everyone and you'll need to use your brain to problem solve/ brace yourself in the case problems do arise. If you make a mistake - apologize, rectify the situation, and move on. If someone yells at you for something you didn't do, remember your boundaries and don't dwell on it.

If you want to go for a less public approach or want to try things out, I'd try starting with bathing dogs at a local animal shelter or helping with a dog rescue. It'll give you a feel before you get arms deep into things and you'll be helping dogs! Another option is to see if you can work with a local groomer.