Hmm - that's a tough one. I'd definitely do spay/neutering for free, and perhaps vaccines. For other issues such as illnesses and injuries, I would be inclined to charge a nominal fee. IMHO pet ownership implies taking responsibility for the animal for the rest of its life, and I would want my clients to care enough to pay something, even if it's just $5. Maybe it's because I've spent so much time working in shelters and seeing the results of the folks that don't care and cast off their pets like old clothing. 😡