Selling (giving away) photos

As some may remember, I have been shooting for the local roller derby teams for the past year. The skaters, officials and the many helpers are all unpaid volunteers. I usually hand out some free (Sams Club) prints to the skaters and they seem to enjoy receiving them. This year they have asked if they could reprint some of my images and sell them at the events to help with their overhead with no compensation to me. I am inclined to agree but I'm interested in your opinions. My friend advised against it.

Here is a shot from last season.

mhb