Tammy, did you provide him with a quote or even suggest a %? Quite possibly he was shopping. I personally don't provide fees without going into the office analyze the practice ahead of time. I do know billing companies to somewhat quote 6-10%, etc.. personally I do not do that at all. I analyze the practice, analyze and estimate time involved, supplies and expenses and then they will get a quote for a monthly fee which will also spell out my sliding scale.
Many billing companies make a big mistake going in there with some sort of quote because they can shop around and your lost in the dust because you gave a quote, the lower quote/bid is going to be first entertained. You won't get a chance to sell yourself by quoting your charges right off the bat.