1) CUSTOMIZE YOUR E-INFO
Offer a customized e-information product instead of writing a whole ebook and guessing what info people will buy. Just let them decide. You could charge people to e-mail you five to ten questions that they want answers to.
After they order, take them to a private web site where you would have a special e-mail address or form they could use to e-mail you questions. You would then e-mail them back answers to their questions. If you're an expert, it will be pretty easy to answer questions without any research.
You can also get away with charging a high price for customized information. You could charge a one time fee, per question or even a subscription fee. You would have to limit number of questions they could ask every month unless you have a big staff.
2) CHARGE FOR UPDATES
Create an ebook to sell for a one time price. Then inside ebook sell subscriptions to monthly updates of ebook. You'll make money up front and still have a chance to make residual income. Plus, it's an instant back end product.