Never do anything on faith or as a handshake deal. Always ensure you get paid (hint: escrow is kryptonite for weasels). Trust everyone, just not the devil inside them.
Also, mandatory: https://creativemornings.com/talks/mike-monteiro--2/1
Also, mandatory: https://creativemornings.com/talks/mike-monteiro--2/1
The lesson I learned is that it doesn't matter how long they've been your friend, when it comes time to pay, they may still try to stiff you. The value of your service diminishes infinitely after it has been performed.
Choice quote from the linked talk (aptly titled "F*ck you, pay me").