First...I agree with most of what you say. It's all got to be a two-way street. Equal = Equal. Like all such things "signage" can seek to control how things work.

In this case, if you are in business, but choose to be selective in who you will or will not serve, you should just put up a sign. Bakers or web designers or restaurants who have limitation on who they will serve should state that. Put up a sign. Let people know..."we reserve the right to refuse service to (put in whatever you want). Tell me and I'll happily go elsewhere.

That idea is tenuous though and likely discriminatory and thus somehow against the law.

There is another choice....just go somewhere else. Find another baker or web designer or restaurant; though cancelling 1 hour before the reservation makes that problematic, and brings me back to signage. If you won't serve certain people, yet don't make that clear beforehand, it becomes your problem, not the customers.

The ubiquitous "No Shirt, No Shoes, No Service" signage may be a dissimilatory action against the "Church of the Semi-Naked" whose members believe shoes and shirts are tools of the devil. But they rarely patronize such establishments because the signage makes it obvious they will likely not get served.

Or, like when purchasing a gun, the restaurant could require a background check on all reservations...or maybe even customers at the door.