Although we do not encourage selling your POAPs, we do not prohibit the activity.
Before selling a POAP, you should first recognize that POAPs are meant to act as the bookmarks of your life. Each POAP is a record of the memory shared between collectors and issuers; something precious, to be treated with great fondness. To sell them is akin to selling a childhood photo, or some other personally sentimental memorabilia. To buy them is akin to purchasing someone else's concert ticket and pretending that you yourself had gone.
With that being said, some POAPs can be worth quite a lot of money on secondary markets, and if someone is able to pay their rent or feed their family that month by selling a POAP, they should be free to do so.