Treating people the way you want to be treated does not work in many cases. I have found over the years being nice get's you in trouble (screwed) more than often than you would think. There are too many people that do not give a shit about anybody but themselves! This is very unfortunate because being prick can get you the same. Somebody mentioned putting charges in initialy. That is whAT you need to do! Unless it is a builder you always work with and you know for sure he will take care of it, put it in the contract. Drywallers often hire cheap labor.
In my opinion it doesn't take much skill do hang sheet rock. That is why the workmanship is so poor. I could hire labor for low rates, but I would loose my customer's in the end.