We have this system at our schools, too. It was implemented several years ago...easy child was in elementary school and he's a junior in high school now. The first year or two, I had to stay on top of it. easy child wasn't buying lunch for anyone else, but the cashiers hadn't been properly trained and they were posting his money to others accounts and charging him for lunches he didn't buy, etc. At that time, easy child didn't buy lunch, just a milk, so when we kept getting notices that his account was low or overdrawn I would ask for a transcript of purchases.
It happened all the time initally. I asked them how they were going to get through the state audit (the state auditor's office audits all agencies that receive public funds every year) if they couldn't figure out how to do the lunch money. What really ticked me off, is they didn't give you a choice. So, if I didn't have any change and gave easy child $1.00 for milk they wouldn't give him change...it would just go into his account. When they couldn't get it right, that really annoyed me. They've since worked out the bugs, though.
Now that he's in high school, I've checked his transcript a couple of times when it seemed he was going through money too fast. A couple of times he has bought lunch for his friends (which I don't mind as long as they pay him back), but mostly it's the ala carte items he's buying. Or not buying the regular lunch and getting something else instead...pizza, nachos, whatever. It is expensive. If he buys a powerade in the lunch line it's $2.00, but if he buys it out of the vending machine it's only $1.00.
I'm sure there are some limits that can be put on this. I would take it up with the cashier and then the food service supervisor if you don't get anywhere. $96.00 in 10 days is ridiculous. Someone should have caught that.