I dont really know of a valid solution to fix this problem and it is probably partially my absent mindedness
but I spend quite a chunk of change on coins for my ad threads and stuff so I tend to get a lot of threads upgraded to red/bold that after a while go inactive and I dont bump them but they continue to get charged for upgrades
maybe make a confirmation system of some sort so if it has been on auto-upgrade for 3 weeks it will ask before doing it again?
I logged in today after not having bought coins in a week and it immediately spend like 30k of them
most of which were on old inactive account for sale threads