I'm rather amazed that with all the various places I've used cards at restaurants, and the fact that they have to go back and put in the tip amount, etc., I've never been double billed. While I don't eat out every night or anything, I've used it enough at such places, even moreso over the last few years, that having never experienced a double billing leads me to believe it's pretty rare.

Now, I don't know if this automatically casts more suspicion on your neighborhood small operators. Maybe, maybe not. Maybe the reality is that they aren't training the people as well, and thus those people are screwing up more often. Or maybe they are deliberately pushing it. I don't think they could continue to get away with such deliberate practice, though. I think enough people would notice and complain, and if they had enough disputed charges someone would get suspicious. I always check my statements against receipts and would notice this right away.

One less malicious odd thing happened just a few weeks ago, with a really small place that actually says "Sorry, we can't put tips on your credit card": they didn't close their batch until 2-3 weeks later! So charge was like June 3 and posting date around June 19, something like that. No issue with the amount, though.