You may not know what list suppression is, so I will explain. If you had a customer list of say 30,000 and you wanted to buy another 100,000 you should do a list suppression. This is how it works, you would send your customer list, to the list company, and they would suppress the list that you are buying so that it does not include the 30,000 customers on your customer list. So instead of getting only 70,000 new names, because you are purchasing names that you already have on your list, you will actually be getting the 100,000 that you wanted. Combined with the 30,000 you already have you will have 130,000 names.
This is one of the reasons that we like to be involved at conception, so that we can advise customers on how to make the most of their list purchase, designing for postal specifications, printing and how to get the lowest postage. Consultations are FREE for our customers.