Sounds like a good idea, just so long as everyone understands they participate in such trades at their own risk, and that Dhamma Wheel is not responsible for any unsatisfactory consequences that might arise because a trade doesn't pan out as intended. I also think that it's reasonable if people just want to give books away that they can ask the receipient to pay for the postage if they wish to do so.
“I hope, Anuruddha, that you are all living in concord, with mutual appreciation, without disputing, blending like milk and water, viewing each other with kindly eyes.” (MN 31)
What is the final conviction that comes when radical attention is razor-edge sharp? That the object of the mind is mind-made (manomaya). (Ven. Ñāṇananda)
"If you have always believed that everyone should play by the same rules and be judged by the same standards, that would have gotten you labeled a radical 50 years ago, a liberal 25 years ago and a racist today." (Thomas Sowell)