As usual, Virginia Postrel is right on point. Speaking as someone who doesn't have a dog but doesn't hate them, I've seen both sides of the issue. If I were a small business owner (which I'm not) and someone walked in with a dog and one of those vests, I'd ask for an official copy of the certificate. When they couldn't produce one, I'd ask for them to leave. I'd do that knowing that there would be an attempt to "cancel" me by enraged dog owners.
As usual, Virginia Postrel is right on point. Speaking as someone who doesn't have a dog but doesn't hate them, I've seen both sides of the issue. If I were a small business owner (which I'm not) and someone walked in with a dog and one of those vests, I'd ask for an official copy of the certificate. When they couldn't produce one, I'd ask for them to leave. I'd do that knowing that there would be an attempt to "cancel" me by enraged dog owners.