Catalog recipients complain a lot about mailers making equally basic mistakes. I have received some of those complaints in the past and had to dig into the nuts and bolts of direct mail. Two common mistakes: mailing to people who do not want to be mailed, and not getting mail through to people who do want it.
In business-to-business marketing your models can be misleading because one large company can have many contacts interacting with you in different ways. If you run your model at the contact level you might overstate or understate the value of any one contact and miss the overall value of the company or mail the wrong people.