Well, it depend in what kind of e-book you're selling, what customers you're targeting, and what value those customers may see in your e-books.
Many books on marketing, money making, DIYs, recipes, and so on sell very well. If you're selling your success story as a marketer or a business, then it is likely to gain more readers. If you're an established author and have a lot of loyal readers and supporters, then also your ebooks will sell better.
Also particular niches gain more readers. Some are looking for good books on medical conditions, so a qualified medical personnel who writer an eBook on health issues, their cure, and prevention is likely to see their ebooks sell better.
Any expert of their field are to gain more loyal readers and so their ebooks will sell with good sales.