While I find this story incredible at face value and have no reason to doubt the OP in his take on it I do wonder when such a huge disconnect is made known what is the info not said.

A few comments- 3000 a year of any condition riding can and does wear out BB bearings many times. The press fitted cartridge bearing seals don't always do the best at keeping out water. I'd be very interested in seeing the "bad" bearings to know the actual "failure" mode.

I agree that miss installed cartridge bearings will hasten their demise. And add possible bearing seat damage. But there are work arounds to this often, if seat damage did happen.

It's a well known issue of press fitted BBs that proper initial machining of the seats is vital for best performance.

It would be interesting to see a copy of the service sales slips (shop ID can be blanked out) to see what actually was done at what cost. We reprint service tickets for customers sometimes for them or for our needs. If the OP didn't save the original slips (and if not then bad on him) he might approach the shop and ask for the records so he can track his costs. Andy.