You're a client who has employed an ad agency to build your business. (There's really no other reason to employ one, after all.) You want more sales.
Now, there are many ways that you and your agency can go about that. You can generate more awareness of your products, which is the traditional "mass" method. You can generate more engagement with your brand, which is what digital can do so well. You can try to acquire more prospects, or retain the loyalty of your existing customers, both of which are direct marketing strengths.
But what you're not looking for is someone to tell you that your microsite needs to be in flash simply because it's cool, or your TV spot needs to be funny simply because the creative team wants to win awards, or your DM piece needs to have an awesome and complicated format simply, well, because. And unfortunately, too many creatives walk into client presentations believing exactly those kinds of things as their basic reason for being in this business.
They're wrapped up in their own craft – the words and the pictures. Each is a craft that isn't easy to do well and each requires real focus. Somehow, in all that focus and intensity and passion, it's easy for creatives to get isolated from the client's real purpose. (And come to think of it, from the consumer's reality.)
Too many creatives don't fundamentally believe it's their job to help you sell your product. Too few think that they will have failed if your sales don't increase.
Creatives need to understand that they're in business. Your business.
What can you do as a client to ensure that you're working with folks like that? Before you hire an agency, talk to the creative director and team you'll be working with about your business. They're not going to be experts at what you do, not yet. But are they at least interested in it? Do they ask questions about it? Do they listen to what you're saying and get excited by it?
And find out about how they work. Will you be seeing the creatives at every concept presentation? (Some agencies tend not to let the creatives out in public, which fosters that isolation.) Do the creatives have input on the strategy? (Some places hand creative teams a brief and expect compliance. Other places give the creatives equal responsibility in the development of strategy, and expect questioning.)
The more that the creatives are at the table with you, talking about your needs, showing your their work, hearing what you have to say about it in person, and accepting responsibility for the results, the more they'll know your business, and the more you'll be sure you're working with creatives who truly want to build your business.
I can't imagine a better partnership than that.