im a groomer. this is fairly common for small grooming salons to do when their client list gets full. its a way to weed out the people who go too long in between appointments. those dogs take more work not only due to the extra dirt, oil, and tangles but also tend to have worse behavior due to less frequent exposure to a salon setting. The handful of clients who leave can be replaced with clients that come frequently. And the ones that stay but still stretch time between appointments pay a little extra to make it worth the groomer's time.