It's all a bit like paying for e.g. groceries based on how you treated the checker.
Treat him/her nicely or neutrally: pay regular price.
Treat him/her rudely: pay inflated price.
Not the way the world works, nor should it.
Slightly off topic, but I saw a sign in the plumbing supply store the other day that I thought was pretty good. It said:
OUR RATES
$50 per hour
$75 if you want to watch
$100 if you want to help
$150 if you tried to do it yourself first, but couldn't
