Most lists are rented for a one-time use only.  There are many compiled files that offer the marketer the opportunity to rent the file for a 2 time use or even for 12 month unlimited usage.  If a prospect from a list you mail responds to your offer, that person is now yours and can be added to your house list without any additional requirements on the part of the list owner.  But never hesitate to ask us about a special use case, a reuse of a file, etc.