Can you sell a provisional patent?

A provisional patent application is intellectual property, and yes, you can sell it. One simple way to do it would be to execute an assignment - you agree to assign the rights to the provisional patent application to another party, they pay you an agreed amount, and you have the assignment recorded in the patent office. In the US, recording of the assignment is free provided you file it electronically - if filed in paper, the charge is $40.00.

Sorry Simon - with all due respect, you are wrong - I recently spoke to the USPTO assignment branch - if you file the assignment electronically, there is no charge - if you file in paper, there is a $40.00 fee. In fact, even if you file electronically, for example, with all of your original application papers, application branch will not electronically transfer the assignment documents to the assignment branch - believe it or not, they print out your electronically filed assignment documents onto paper, and send the paper to the assignment branch - therefore, when assignment branch actually receives your assignment, to them you filed it in paper, so you still get charged the $40.00 fee. To get around the fee, you have to specially file the assignment directly with the assignment branch.