It's not hard. As an owner, we always dive and check the keels on the first day there. If you see chunks gouged out of the keel's leading edge, then you know that someone "grounded her in the last year or so without reporting the incident." We were with the same charter company as Salica and they did not routinely dive the bottoms. Most companies don't, but a lot of charterers damage boats and never report it, since they figure the charter company won't find it for a while and won't know which charter party did the damage. We often found gouges in the leading edge of one of our keels (catamaran). Burned me up every time but not much we could do about it! We would have to pay for the repair when it was hauled for painting, and it was usually below the insurance deductible so not worth reporting.