If it was just a letter about the service being poor, then they would probably have a talk to the crew and ask their version of events. If there were no other complaints from passengers on that flight and no complaints about the crew from previous flights then yeah, they would probably just write it off as the pax and/or crew were having a bad day and send the customer a form letter and leave it at that.

But the the matter of the cabin not being properly secured for landing and a trolley coming rolling down the isle, possibly hitting a passenger on the way? I imagine that this will be taken very seriously indeed. Poor customer service is one thing, compromising passenger safety through sloppy working practices is quite another...

A well written letter, IAMORGAN.