To answer your question, I differentiate myself by providing top notch customer service & being a relatively down to earth guy. I make myself available to customers most of the time and I guess they appreciate it. I also am pretty well known for being successful in business in general (for my marketing firm) and word spread.
That and I brand the hell out of myself & have made friends in the community that have helped quite a bit.
I also have a mailing list of all the people that have bought my products, so I can bring quite a bit of attention to a new launch very quickly, which kind of creates a cascade effect to bring in more sales.