The product I make is a very specialised system in the agriculture industry. The first 10 customers were a mix of old clients from a previous job and new clients who read about the product from an ag news source. I had to rely heavily on my personal reputation in the early days but that has become less important now. I also hired a sales coach to help me (technical background) break through my limitations in closing deals. One interesting thing was the original direct sales model was terrible, drove 45,000km that year around my country doing delivery and training to ensure those customers had the best chance of success. Sold some gear to a customer who rents the equipment out and all the subsequent growth came from that model.
Those first customers didn't turn out to be as critical as I thought, the real change came from finding a scalable business model. There was no way I could have continued what I did that first year.