I have a spare license that I am not using and am unlikely to again. If I can find a buyer am I allowed to sell the license to them and transfer ownership of it? 

Nope.

https://invisioncommunity.com/legal/standards/#transfers

  Quote

License Transfers

All Invision Community licenses are non-transferrable. Client area accounts may not be shared, under any circumstances, with a third party. Licenses purchased through a business name may have the contact information updated; please contact sales@invisionpower.com for more information.

 

Thanks for the input. 

Well that sucks. Another thing to dislike about this company.