This looks like a case that should be reported and acted on, but there are also cases where people complain unnecessarily.
I saw a case recently where a buyer left a negative for an item with $10.00 postage and complained it should have been $7.00 postage but did not allow for handling, cost of packaging etc.

With my postage costs I guesstimate everything as if I had to weigh every item individually or take it to the post office I would need to add five dollars to everything to allow for my time and wasted effort.
Sometimes I make a dollar or two and other times I lose a dollar or two.

so there is balance in everything.