Things are done differently in my neck of the woods. No money changes hands unless a form 4473 is filled out.
Form 4473 says that the NICS check should be done immediately prior to the transfer, and if the transfer takes place later, there must be a re-check immediately prior to the transfer.
So, you can sell the firearm before you transfer it, and then do the 4473 at the time of transfer.
This accommodates a waiting period, which many states have.
It also accommodates online sales, where the gun is sold first, and then picked up later via an FFL holder.