The word private in private label SEO pertains to the actual firm itself. While the firm is a private company, just like most SEO companies, the term is mostly associated with the overall notion that the firm hopes to be kept under wraps in gaining any sort of recognition for its work.
This intention is directed more toward the general public because the average private label SEO will market itself to actual marketing agencies and advertising firms. It also hopes to get Internet and web design companies, who know better than most about the beauty and the power of SEO.
The typical private label seo knows that its work is essentially done for it with these resellers. These resellers have easy and natural ways to group SEO with their other marketing, web design or advertising services. So the time between initial contact and the final sale is pretty short here.