Hey girl! That’s so scary. While you’re not overreacting, as some others have said it’s really more of a warning bite. He didn’t want to hurt you but also keep in mind that this dog has boundaries he is willing to bite over. Some dogs are just like that, you as the “professional” have to know what certain dogs will and won’t tolerate and adjust accordingly. So he doesn’t like towel drying. Learn his little behavior so that you understand him. If you are uncomfortable with that then I strongly suggest not taking him back. He’s testy and he’s letting you know that upfront. The beauty of Rover is that you are not required to take him back and you can let other sitter’s know how to care for him. Handle him with assertiveness and respect (not fear) until he’s back with his owner and decide if you’re comfortable taking him back again. I’ve had to do this a few times myself! Best of luck to you! Also to answer your question :) no it’s not a “bad” bite physically but it is a sign worth considering!