Marketers of all stripes are discovering that acquiring a reputation and permission to market to people isn’t as expandable as they might hope.

A PR firm, for example, might have some terrific clients. These clients give them credibility to talk to the media. Over time, the firm gains a reputation with bloggers and other media outlets. Emails get answered, press releases get read. The clients get ink, new clients show up.

The temptation is to grow the business. To take on new clients. To do the PR magic for an ever larger group of people.

Here’s the problem: the people who most want to be your clients are the people you should least want to represent. As you promote the unpromotable, the permission you have to talk to the media doesn’t go up, it goes down. Better to be the agency that only represents bestselling authors than to be the biggest agency.

In the long run, the pickier you are, the better you do. Same thing goes for online merchants, brokers, church groups and just about anyone else who markets with permission.