It is going to vary alot. Most bathers are paid by the hour, but some are paid per dog. Some bathers strictly bath and dry, some do brushing, nails, ears, etc. Some bathers are required to also clean up the entire salon. My bather just washes, dries, and cleans up the bathing room, including filling shampoo systems, wiping down walls, mopping floors, etc. She is paid hourly. I would say generally, in my area, wages are usually from $7-12 an hour.
It will vary...depending on the shop, you may also be paid by the dog; a certain percentage. This can be a good and a 'bad' deal, as if it is really busy, and the groomers need you to bathe alot of pooches, you can make some decent money in a matter of hours; but on the slow days, you won't make as much; which can make being paid hourly better. It will depend on the shop though.
No matter how you would get paid, I highly suggest going in and observing what goes on in a dog grooming facility before diving in head first; especially if you have limited experience with dogs.
I would consider 7$ an hour if you are a teenager with no experience....that is really low for the amount of hard work....
I notice that bathers usually do not make a good hourly rate, but stick in there if they want the experience to go on as a groomer. That is the only reason I did it. 5 years ago, I made about 8$ hour as a bather. I would think it would be higher now. It is not easy work.
If I were to hire a bather I would pay them at least 9-10$ hour.