This dog I have now is not potty trained, is very wild and overly energetic, jumps everywhere, and has all features of a puppy. However the guy charged himself for a dog rate.
Did you have a Meet & Greet before you accepted the job? If you had, then you might have seen the puppy-like behavior. When a dog matures depends on the breed. As a general rule, small dogs complete their developmental phases in about a year, but larger dogs can remain a puppy for over 2 years. Also do you specify that a dog must be house-broken in your profile? Did you go over that with the owner? Could the dog be "marking" and not pottying? Remember, it is always up to you to control the billing and rates Just because an owner filled in the regular rate, does not mean you cannot amend it based on your own observations and experience.
How old is the dog? Usually I just deal with whatever problems myself the first time, let them know their dog was challenging after the stay (in a nice way, like "wow Spot has so much energy! You must have a lot of energy to keep up with him. :) He really kept us on our toes" instead of "your dog is way too hyper"). Then, if they want to rebook in the future, charge whatever your puppy rate is, and let them know you're tweaking the price to account for the special love and care that you give the dog. This is all assuming that you would want to have this dog back. There is always the option of saying that the pup is too much for your time and abilities. I agree with Karen that the dog sitter/host is responsible for checking the rates and making sure to set up a meet and greet if there are behaviors you would charge more for. I've lost a little money by not double checking the rates before finalizing the booking (some owners adjust the rate to negotiate), and since I rarely do meet and greets these days, I expect the worst and deal with whatever comes (so far so good). (I wouldn't recommend this approach unless you are very confident in your dog skills and have a lot of time to manage tough behaviors.)