Honestly, I feel like if you opt for “adhering to what sells,” and you lack real passion for whatever that topic would be about, then you’ll just be selling yourself short. Always go with what you love, your passions and what you know, and if you can mix in what “sells,” then all the better. But a lot of times, when we start a blog writing on something we aren’t really interested in or passionate about, it’s so easy to lose interest or not put your heart into it, and readers can tell. In cases like that, you don’t really gain readers, especially long term ones. Plus, you have to be careful when writing about “what sells,” depending on what you mean by that, because blogs like that often appear spammy.