Please contact WHMAP (Brandee) and ask him to verify by posting here that you have permission to sell this license. In addition, could you please clarify what you mean by "unlimited upgrades", as I'm not familiar with that particular license.
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Xabi, WHMAP licenses have been sold on the basis of 6-12 months free upgrades and support included in the license, with additional upgrades and support requiring additional payments. Unless you have some special arrangement or have a license bought prior to July 2003, you will not have unlimited/lifetime upgrades. Please clarify this and when you contact WHMAP please ask Brandee to confirm this as well.
Contact after the sale must be made since the license number that is being transferred is 'disabled' after the sale and a new one is issued to the new owner. This is to prevent 'mulit-sales' of the same license.