Bills that multiply without a plan change
Documented cases include a bill moving from roughly $119 to $854 a month, and a widely shared account of a bill going from $4,000 to $9,000 a month. Because you pay per resolution, success with the product directly increases the invoice.
You buy credits in advance and set a hard cost cap. The maximum you can be charged in a month is a number you chose, printed on your billing page before anything runs.