admin answers:

You really did not give much information to work with. If you are talking about one of those resellers who buys names from the registrar so they can make a profit then…

Use a credit card to make the purchase. This way if there is no transfer, you can dispute any charges.
The domain name is yours permanently as long as you pay the yearly fees to the domain name registrar, and this should not be the reseller unless there is some strange contract.