Anecdote supporting this: When they used DHL in the US, I complained about how bad DHL was for a few reasons. I was told that they would log my complaint, but

Anecdote supporting this: When they used DHL in the US, I complained about how bad DHL was for a few reasons. I was told that they would log my complaint, but there was nothing they would do until enough complaints had been logged. A few months later, Amazon no longer used DHL. (At least in my area.) So it does matter if you complain about their systems.