Most of my friend's favors center around money, so it's hard to avoid dealing with money.
For example: My friend needed some money to buy his wife her Christmas present, I bought it, and he's paying me back what he can, when he can. Than again this guy is practically a brother to me so that's a bit different.
Most other circumstances, a friend does me a favor, I'll return the favor eventually.
In your situations...
Builder: Pay the cost they would charge anyone else(If it's their job), if they're doing it as a favor/hobby, at least pay for the parts and throw in a little bit for their time.
Waiter: I wouldn't treat them any different other than maybe the conversation I would have with them. Than again, I usually tip decently if the service was good.
For example: My friend needed some money to buy his wife her Christmas present, I bought it, and he's paying me back what he can, when he can. Than again this guy is practically a brother to me so that's a bit different.
Most other circumstances, a friend does me a favor, I'll return the favor eventually.
In your situations...
Builder: Pay the cost they would charge anyone else(If it's their job), if they're doing it as a favor/hobby, at least pay for the parts and throw in a little bit for their time.
Waiter: I wouldn't treat them any different other than maybe the conversation I would have with them. Than again, I usually tip decently if the service was good.