It's often said that you shouldn't meddle with things you don't understand and, by extension, you shouldn't mess with the people who handle the things that you don't understand either. If you've managed to get a contractor in to handle something you can't or aren't willing to do or understand, and they deliver on that product, you'd do your best to pay them the agreed price. After all, we've already established you don't understand that thing, so why are you so certain you've got the upper hand…