Freesound Forums

I have a number of sounds uploaded here under the non-commercial attribution license. Someone has offered to buy a commercial license to one of the sounds--what exactly is the procedure for providing permission? Do I need to provide some sort of contract? Or, for example, is it sufficient to send an email that says "I [full name] (aka freesound user 'damnsatinist') give permission to (other user) to use [sound name] commercially" ?

I had to do this once for one of my sounds. The other party insisted on it being a written contract.

A contract would be the ideal, you could get away with written permission, but you might want to go the extra mile just for assurance.

Here is a standard music license agreement:
https://nimia.com/wp-content/uploads/2015/04/Standard-Music-License-Agreement.pdf

I could send you the contract that I had to sign. Private message me if you want this, i'll be happy to share, because it's a little more specific to your case.

There are also, many artist release form template on the net. So you can find, or create the one which suit you and the other side the best.