Sounds like some of you would make great lobbyists for the Veterinarians.
My dogs are on heartworm preventative that I get from Canada, a whole lot cheaper than what I pay at my vet. He’s a rural vet and doesn’t require a test to buy it. I had him test a stray great Pyrenees and he just pulled blood and looked at it under the microscope. I think he figures more people will use preventatives if it’s simple to get. He knows they won’t if it’s costly and difficult to get. Most of his clients are lower income, or people without a lot of disposable income.
Years ago when I worked for vet the salesman told me that really heatgard (what he was pushing) is good for 2 months. They were running trials to see just how frequent you needed to give it.
I’ve known lots of people who use ivermectin too. I just have collie type dogs so don’t do that.
My dogs have never been checked for heartworms. They live nice long lives never being tested.