If they blow you off with simple questions, I expect they would show the same disregard if you never get what you expected. If you want to do it for practice, go ahead. I'd call burlap on top of cotton as embellishment. I really could not reccomend it as a piecing fabric - too loose a weave, and would unravel when washed. Consider it a donation.
Swaps are notorious for attracting predators who get what they're after, then drop off the face of the earth. Perhaps, if dealing with strangers, you all could post pictures of your progress. Besides having the fun of seeing what everyone is doing, the ne'er-do-wells will run out of excuses and the person swapping with them can be forewarned. It happens so often that I have become jaded by people who pop up, want to boss others around, or jump to get stuff, then disappear without so much as a wave or a nod.