Good friends don't ask for a discount
There are two reasons why we hire our friends. First, we want someone we could trust—we feel calmer that someone will go an extra mile to do a good job. Second, we want to save money, and if we’re lucky enough, we might get away without paying.
It’s easy to spot that these two reasons contradict each other. Paying your friend well—even more than it would normally cost—makes them feel valuable. It’s a way to show your respect and admiration to them and the work that they do.
To ask for a discount means to pay with your friendship. Your friend might still do a good job, but paying less (or paying nothing) is an overt attempt to take advantage of your friendship.
Pay your friends well, because work is still work, regardless who does it.