[user5994461]

That's not a good comparison. The rental market always had a big part of black market through local listings, mouth to mouth or sites like craiglist/gumtree.

The regulator/IRS could go through some residential blocks in popular cities and find undeclared tenants in almost every house. AirBnB makes it worse and shorter term but it didn't invent any of that. It just makes it more visible.

In comparison, restaurants are rarely undeclared or illegal operations.

[djur]

Also, unlike AirBnB, even a conscientiously-run underground restaurant would have trouble not attracting attention from my neighbors. If the house down the street has a different car in front of it every week I would never notice. If there's a constant stream of people visiting (parking on the street, etc.) I'd notice and probably be inclined to figure out what's going on. That pattern of behavior is also likely to get the cops called on suspicion of drug dealing.

I think a very, very cautious person who carefully screened their clientele could get away with having one, maybe two small groups dine at their house a night. Probably not even every day a week. Suffice it to say that we're talking about a market so small it might as well be said not to exist, and by that point you might as well just call it catering or a private chef, not a restaurant.