Do they really do this for pet owners that otherwise couldn't afford it (i.e. do they means test the clients to see if they are in financial difficulty?), or is it just owners who want something cheap? This is a significant issue in the veterinary clinic world.
So all spays and neuters are done pretty darn cheaply. Plus they occasionally get grants from places like PetSmart to do like 200 cats in February for $20 each as cost to owners. Currently there is a "all outdoor cats in Loveland" special going, but I don't remember the price. They get grants to cover around 100 Pit bull spays and neuters for insanely cheap and Chihuahuas on another.
Yes, we/they occasionally get someone driving up in a Bentley to take advantage of the price for their pure bred poodle. We bitch about it too. But we also ask those people to donate to the shelter, clinic, TNR program, pet food pantry...
In order to get free surgery and free or discounted vaccines, free food, and occasionally assistance paying a bill at another vet clinic (I'll explain in a minute), you do need to prove need. The easiest way they have found was letting the government do the background check and we just verify that they are on some sort of government assistance program. They have to spay or neuter EVERY animal in the household. Which means nobody gets to live under the theory that they can make money breeding mongrels in terrible conditions. Hoarders are often gently talked into giving up many of their animals to the shelter or to a local rescue. But elderly and low income people who have fallen on hardship have a way to keep their animals. They have to verify that they are still on assistance every so often to continue on the programs. No new pets unless a previous one died. They try to work hard to make sure that they are helping, not creating a problem.
They have had to create limits on what the clinic can offer for care from the moment they opened their doors so that local vet clinics didn't throw hissy fits about stealing business. (At least some are glad they can send the guy who can only afford $100 for a neuter on his 150 lb pit cross somewhere else rather than having to extend some sort of credit that will never get paid, so they can concentrate on the more able to pay clientele.) But, part of the Prevent a Litter program is allowing low income owners with an emergency to get at least a little help elsewhere too. Classic example: 8 year old Pom presents at the ER with a pyometra. Owner is a older woman with obvious poor dental care and a handicapped child. She has no money but brought her dog in anyway with the last $120 to her name. At the ER that basically only covers an exam. Fixing the pyo plus post care would run about $3000. Sent to the clinic, emergency pyo surgery is $250 out of pocket plus $100 for overnight monitoring with a different local ER that has worked a deal out with the rescue. Or, since they are low income, with the PAL program, in this case they donated $80, but owed nothing and we're sent to the referring ER for post op overnight care on fluids with up to $250 in care covered.
Everybody won because the dog got to live, the ER got more money than they would have and the money came from a program supported by donations and grants.
I know a lot of this will be argued about. I tried to explain clearly and quickly and those don't often work hand in hand for hot button topics, but these people really try and have been at it over 10 years so they have worked out a ton of kinks and had to do a lot of diplomacy with the local doctors to keep going.
Full disclosure: I worked at both the ER and the Rescue Clinic during this story so I can really go into numbers if you want, but everybody really was happy at the end.