To add something on a more positive note, I once turned up for an exam only to find that they had a problem with their servers and that the exam was not available. Three hours later when they'd resolved the issue I said that I now didn't have time to sit the exam (had only booked half a day off from work). To their credit, I was offered a full refund or the chance to reschedule (I opted for the latter) so I guess it comes down to the staff at individual test centers rather than Prometric as a whole.

Regards

Lempster