If your clients are requesting ebooks, then you already have a platform to sell to. As Lydia said, your sales will be reflected by how well you are able to market yourself. Sometimes writing is the easiest part. Price your books reasonably and let your clients know about them. The best books to write are those that solve problems for others; books they will refer to over and over. If they find the books helpful, they will tell others. Word of mouth advertising is best. Perhaps you could include some client testimonials in your books as well. Oh, and with the POD options out there, don't limit yourself to ebooks alone.