Regardless of your interpretation of the various parts of 14 CFR (just google it and enjoy the rabbit hole....), the FM1 says no outside flying for reward. If it’s ever changed to “....except for CFIs” I may pursue it but honestly who wants to crawl back into those little sweat boxes lol.
That said if your friend hits you up for a flight review and you do it pro bono and you accidentally forget your wallet later that night at the steakhouse he took you to, who’s to say....