I would tell my friend that after looking at it and consulting experts (us), you think it is worth only X (rock bottom lowest potential selling price that you determine after looking at a bunch of other listings) so you will put it on Craig's List for that amount. Without any further investment of time or money.
Notify him when someone is coming to look at it - he can come over and meet them. Also tell him if it doesn't sell in a month, you will give it away to anyone who will come and haul it away.
If he disagrees and protests, tell him he can pick a storage lot, he can pay to have it towed there, and he can pay for storage and take his own sweet time getting a better price.
Or he can start paying you rent until it sells. You might be doing your friend a favor by helping him learn how to be an adult.
