If you are looking to be hire, or hire someone to do work for you, general rules that should be followed:
Have a written contract - this is a good starting point. This is very important. You must specify the exact scope for the work, and the expectations. The contract can be signed digitally.
Pay half up front, and make sure you're paid half up front.
Clarify what licenses are required and paid for
If there are addons in use, has the author given permission? Have the licenses been paid?
COPIES OF THE LICENSES ARE REQUIRED TO BE HANDED OFF
The rest should be paid upon delivery
Don't be a dick