They are also looking for an edge over their competition. When networking, first impressions, obviously, are very critical. When potential customers are receptive and allow you to approach them, they will, in most cases, only give you a few minutes of their time. Upon initial contact in those few brief moments that you have their attention you are trying to accomplish a lot. You want them to remember you and ultimately you want a sale.
Time is critical to everyone and people are very protective of it.
Remember that and respect that. Chances are your potential customer wasn't even expecting you in the first place. Approach them with that in mind. The business card. People like pretty things.