I offer refunds on unused hosting; but I do allow clients to transfer their accounts to someone else - particularly in cases where a site is popular, is managed by several people, but only one person at a time is in charge of paying the cost.
I ask them to submit a support ticket and tell me who the new "owner" will be, I ask them when they want the cutover date to be set, and I then email the new person (and cc the old person) asking them to sign up for billing before the cutover date. This also gives me an opportunity to make sure that the new person knows the TOS and agrees to be bound by it, knows about the affiliate plan and has the proper links in place, and is otherwise satisfied with the current hosting plan. It lets me make contact with the new person, assess their needs, and see if there's another solution that might be a better fit (whether upgrading or downgrading). They also appreciate getting a chance to learn what resources are available to them, both in terms of support and alternate hosting options with us.
I personally do not allow "subleasing" all or a portion of a hosting account. That just leaves too many possibilities for problems: the new owner doesn't have a clear line into support, if the new owner doesn't pay or violates the TOS the old owner is still the account-holder-of-record and is thus responsible, et cetera.