Have you ever met an aggressive sales person who pushes and pushes as hard as they can to make the sale, hopefully wearing down their customer enough that they finally give in? Chances are, your reaction to that sales person was not very favorable. Even if you did give in to that initial purchase, you probably never wanted to deal with that salesperson ever again. You stopped taking their calls. You blocked their email address. And you may even have told others to "watch out" for this salesperson in the future. In the end, the salesperson may have won a sale, but they lost your future business.
