Let's take an Italian restaurant site as an example. Your tagline might be: "We have the best Italian food in town!". Your end game would to get people to come to your restaurant to order pizza and pasta.
Most websites are marketing tools. Their purpose is to make money, and this site is no exception. I don't need to tell you that the ads to the right are there for a reason. We have all developed radar finely tuned to marketing and have accepted it as part of our lives. What none of us will tolerate is someone trying to sneak something past us.
Be upfront and plainspoken. Let visitors know exactly what's in it for you or your client. You don't need to be abrasive or pushy, but do not do anything that could possibly be interpreted as being something that it's not. Even if your site isn't trying to sell something, make that clear.
Like navigation, when someone first goes to a site they are subconsciously scanning for that end game. Once they know where they stand vis-á-vis money, they don't have to think about it anymore and they can get on with ordering pizza – or not, as they please.
Trust is hard to come by on the net. Don't squander it.