Yes but not much, I earned $5k+ over the course of two and half years.<p>1. Yes, I am selling ebooks related to iOS development
2. I sell on Gumroad
3. You might have heard this before, but I will repeat it again, build trust with your audience first before selling them stuff, so they know you are actually skilled in your trade and your product is actually worth the money.
eg: if your product is for python dev, then your audience is python dev.<p>To build trust, help people in public, like answering question in reddit (eg: r/python), stackoverflow, write technical blog post that answers common questions etc, I have been doing this for 2.5 years. Then put a newsletter sign up box below each blog post, this way you can reach your audience who is interested on your content directly, very useful when you want to launch product to them, make sure you use it to regularly send useful information to them too, not just use it to launch product.<p>My iOS blog : <a href="https://fluffy.es" rel="nofollow">https://fluffy.es</a> , I have stopped writing on the blog as I no longer work as iOS dev now, but I still get a few sales each month.