Of course. If you purchase clients from one web host, those clients have already become accustomed to how that host does business and how it handles support and other related issues. If your business does not meet and/or exceed the standard that has been set by the previous web host, there is a very good chance they will leave.
A second problem I see with purchasing clients from a customer perspective is that I would feel like I am property rather than a person.
However, if I were to look at it from a web host standpoint, I'd see it as an easy way to get more customers. I would make sure that I treat them better than their older host did to avoid losing some.
All in all, I think it would make people feel less valued as a customer. But, hosts can use it as a quick way to get more clients.