If 1% of the time a customer uses $100 extra, you don't charge that customer $100 extra. You charge them $0 extra because they had a bill cap and it was your job to enforce that cap. Then you raise the price of the service a very small amount so customers pay $1 more on average and that covers everyone's overages (that's what I mean by amortizing across your customer base). Then you go and improve your limit enforcement because you are actually incentivized to do so, unlike in the case where customers are charged for overages that aren't their fault, where you are actually incentivized to cause overages. Customers aren't dumb, they can see your incentives (see the comment by 0cf8612b2e1e in the adjacent thread).