but this won't wash if the last guy made a mistake.
I thought that maintenance was done on the basis that the previous engineer was trusted. Otherwise, everything is back to birth, every time. Whe is the line to be drawn?
What is happening is the maintenance companys who did half the job for 75% of the true price are being outed and the customers of these companys are screaming like stuck pigs because they are now having to pick up the cost of years of shoddy maintenance.
I suppose a lot depends on whether the last company's invoice states what was done, but it can be shown that it wasn't all done. In that case, the MO is liable.
But what happens in the (many) cases where there was tacit collusion between them and the owner (to keep costs down)? I believe this is common in the flight training business, where the paperwork has to look good but the school doesn't want to pay more than necessary. Tricky.....
The other thing is that the rules can never clearly draw the line at the previous service, because that could be used to circumvent a lot of stuff. If you have done an unauthorised (but obvious) mod, you just make sure you change the MO for the next service and they would not be able to question it
I have no idea how this could be resolved formally.