Naver Webtoons does that, though I'm sure it doesn't fall into the category of selling ebooks and is probably well crafted on the legal side. You buy in-app cr

Naver Webtoons does that, though I'm sure it doesn't fall into the category of selling ebooks and is probably well crafted on the legal side. You buy in-app credits, you use them to access series and episodes and download them (you download them in a way that you cannot easily save/copy them). Access is typically revoked a few months later or upon series end, and the expiration of your access rights is not announced. These kinds of practices are why everyone is wary of DRM & Co.