It's helpful that most fancy restaurants are locally owned. Even if there was an attempt at a reservation black market the owner is heavily incentivised to shut it down and because he probably works at the business he owns he can be on top of it.
Doesn't work for ticket scalpers because stadiums don't care who buys their tickets.
Going out for spaghetti is like going out for a PB&J. Of all the minimal effort bottom tier things you could ask someone else to assemble for you…. If I’m paying a server 18% over cost of sale to bring a plate to me I’m at least asking for something that wasn’t made of ingredients most commonly found in a church food drive.