I would start by dropping the "e" part of your requirement. Don't look for good e-books, look for good books.
Then I would drop the strategy of looking mainly at the "deal" books, since at best there is a zero correlation to quality, and at worst a negative correlation.
That said, finding good books is a problem that people have been facing for decades if not centuries, and with mixed success. You've got to kiss a lot of frogs...
Talking books with people whose opinions you trust is a good start. Then there are internet forums dedicated to discussing books of different sorts. There are lots and lots of review sites. One strategy is to find a review site that positively reviews a book you know you like, then see what else that reviewer recommends.
You can also find a library and browse the shelves. Browsing, at libraries and at decent brick-and-mortar bookstores (RIP), is how I found most of the books that I ended up liking the most. Literally at least three of my favorite books in the world I had never heard of until I picked them up from a bookstore shelf (and two of them, I had never even heard of the author).
In a way, reading lists of e-books that are available, rather than going in via a search on an author or title you think you might like, is somewhat akin to browsing. The main difference being the extremely low quality of the ability to spot-read, that electronic bookstores offer. The ability to randomly sample a book's writing in 4-5 places is an immeasurable aid to finding a book you might like, in my opinion.