I have a sim with a restaurant, and he's constantly losing money. Not only until yesterday did I realize what's happening. The guests at the restaurant don't pay their bills! Instead, every time the guests get their food money is drawn from the owner. And then the guests get up and leave without even touching the food. This happens everytime.
I have observed this also. It seems to be an effect of when guests try to eat something even though their hunger is maxed out, because, for some reason, you apparently order food when not hungry. An experimental hack is aimed at resolving this issue, by denying permission to attempt to eat at restaurants unless hungry enough to eat.
The second thing I noticed was when a sim of mine went on a date to a club. they paid for a ticket at the ticket machine and went in. Once inside they didn't buy anything, but I noticed that money disappeared when other uncontrolled guests used the ticket machine.
There appears to be a large number of billing-related issues on community lots. The matter is presently being looked into.