increasing business vs decreasing costs

I have noticed that some advertisements selling to businesses emphasize how much they can reduce costs and some emphasize how much they can increase business.

A VOIP company says it can reduce your long distance fees.

Coffee news for example promotes increased exposure and so more business.

I was thinking trying to convince a business owner that you (a person that does not know their business) can help them get more business is tougher than telling them that you can reduce some part of their costs.

I am selling web design as a way to get more customers but possibly I should promote it as a way to reduce costs (ie. cheaper that YP, less administrative costs answering questions, less unproductive time explaining your services etc.).

When I am trying to sell a business a way to get more customers I feel a little presumptuous. I mean I don't know if their current marketing is working great for them and they are getting a lot of customers.

But I do know they do not have a website and getting one will definitely help them control some indirect costs.