A recent Harvard Business Review blog post suggested that sales reps should avoid customers who are ready to buy.
The rationale is that customers who are too far down the purchasing funnel are probably just using your business for a benchmarking exercise – they most likely have already chosen their intended supplier. According to the article, the better opportunities lie in finding "customers who are going through change and will be open to new ideas...where demand is emerging but not yet established, where they can shape customers' needs, rather than react to them."
While the article is geared towards traditional sales people, it makes sense for agencies as well. Agencies put a huge amount of time, effort and top talent (often at the figurative if not literal expense of existing clients) towards responding to RFPs. So why not task those business development folks with creating opportunities instead of getting invites to yet another crowded party?