ownership of the domain is same as sendoffer.com so you own the domain.
Can't see why this isn't transferable?
Probably what they refer to is you can't transfer the current 'database'.
Worst case new owner makes a new deal with your wholesaler, as long you get the value you want for it.
If you domain has traffic it has value .. not up to your wholesaler to determine if you're going to sell your domain or not.
My 2 cnts.