I'll go ahead and say it: I just object to dogs being every. damned. place. I. go. I'm not crazy about dogs (was bitten badly as a child), do not think they're like children, don't like any animal sniffing me (especially in personal areas -- I'm short) or jumping on me or peeing on plants I might have been interested in buying at the farmers market (yes, I've seen that plenty of times---owners are clueless). There are so many at our market that they and their humans impede foot traffic. I've seen dogfights, too long leashes, arguments and stink-eye.
I've heard people say, "oh he loves to come to the farmer's market! It's so helpful for him in becoming socialized!" Well, that's what dog parks are for, in my opinion, or your own neighborhood walkies.
For a legit service animal, I think people should be able to show documentation at any restaurant or store when they're asked. The vests should not be available on Amazon.