From experience, the bigger risk is not from genuine customers (even though some of them will share it with friends or even post it online for others). The egregious ones are the dedicated "pirates" who purchase the book using stolen credit card data, leaving you with a chargeback penalty fee while they upload the book to websites plastered with Adsense ads so they can profit from it.

Since you can't stop the dedicated ones, better to provide your genuine customers with the best experience you can.