Well, you can point out what makes your business better than other businesses and what is lacking in other businesses that is present in yours.. Always be polite and always be ready to answer questions.. Be confident with your answers and avoid stuttering.. I think these can help you persuade the clients.. Basic things that you must pay attention to..
Always look into the persons eyes. Don't be nervous, Be honest, be courteous, don't be afraid to act human. A little humor is always good - just don't overdo it.
Read You Can't Teach A Kid To Ride A Bike At A Seminar by David Sandler. It gives a very good structure for face-to-face sales encounters. Vin Montello recommended this to me.