Recently I sold one of my Xenforo licenses and I can share with you the whole process so you guys know what to expect when dealing with such task.
1. If you sell your Xenforo license make sure it's active if not there's no way to sell it.
2. To find the buyer post in webmaster forums like ours and put the price on it.
3. After you find the buyer contact Xenforo and tell them this is a license transfer request.
4. After that, you must provide the name, email address and home address of the person you wanna transfer to.
5. You also require providing PayPal transaction ID when you bought it for validation, funny thing here, bought this license back in 2013 and PayPal is limiting searching the transaction history up to 3 years and explained politely to Xenforo staff, after that they require the transaction id from a renewal I made for that license in 2015, I could provide that very quickly.
6. Now the person you transfer the license will receive an email from Xenforo staff to accept their terms of license transfer.
7. Now you should spend the money well
, stay away from h00kers 
NOTE* a license can be transferred only once
1. If you sell your Xenforo license make sure it's active if not there's no way to sell it.
2. To find the buyer post in webmaster forums like ours and put the price on it.
3. After you find the buyer contact Xenforo and tell them this is a license transfer request.
4. After that, you must provide the name, email address and home address of the person you wanna transfer to.
5. You also require providing PayPal transaction ID when you bought it for validation, funny thing here, bought this license back in 2013 and PayPal is limiting searching the transaction history up to 3 years and explained politely to Xenforo staff, after that they require the transaction id from a renewal I made for that license in 2015, I could provide that very quickly.
6. Now the person you transfer the license will receive an email from Xenforo staff to accept their terms of license transfer.
7. Now you should spend the money well
, stay away from h00kers NOTE* a license can be transferred only once
