Spring a high cost on a client they weren't expecting, you get grief. So, when you see an important but nonurgent procedure in the veterinary exam room that needs to be done SOON but not NOW, give them a heads-up.
When veterinary clients pay an annual fee—or monthly installments—for wellness services over the course of a year, will they be mad if they don't use them? Not if you remind them. (You ARE sending out regular reminders for everything, right?)