Welcome to Flyer Talk! Each airline's program has its own rules, you should look up the ones for yours. Some things to consider: How many points do you need for that ticket? Is he going to have to transfer only a small percentage of total points or a big one? If latter, see if it is more cost effective for him to just buy your ticket.

Later Edit: The same point is explained with much greater clarity by tom911 below. Fees etc do vary airline to airline, so do check the specifics for your case.

You already know that in case you are giving any money or any other "consideration" to your friend in exchange, neither of you should mention, hint at or admit it if asked?