This is very complicated.  As for the data; if the ToS stipulates that any member content uploaded to the site becomes the property of the site, then no problem there.  If you are letting members post content where they retain the copyright then that might be a problem with selling the site.  As far as the Dolphin license transfer; that is not possible under Boonex.  There has been people that have sold their accounts under the table and that is hard to trace.  If you did this, then you would not be able to use that Dolphin license for the UNA apps; not sure if Boonex is tracking this or not but the license would be owned by someone else.  Of course Boonex is letting people use their Dolphin license on both a Dolphin site and the UNA site; not sure how they are tracking this.

If you tried to just sell the site files and database without member content, you then run into the problem with the third party modules as the license agreement of many don't allow transfer of the modules either; they are tied to the Boonex account so you can't keep the Boonex account and transfer the modules.  As I said, very complicated.