1. The only thing which clearly marks this as an ad is the comment just above it in the HTML. Which is strange for two reasons...
2. The lack of nofollow strongly suggests this isn't just an affiliate link, but a 'paid link exchange'. Of course, you could just be profiting from the affiliation alone, but I'm sure you are aware as an experience web designer that most search engines tend to frown on this sort of thing.
3. By not clearly marking the element as an advert, you are effectively using one of the same tactics that the "most aggressive and horrible ads" use. Yes, plain text is small font is utter love, thank you for that, but given you've just written a blog post about ad blockers, I'm guessing you must have also carefully considered this
4. You outright talk about "dark interaction patterns" - not labelling adverts clearly is one of them ;)
5. A core theme in your post is "think about what appears on your page and how it affects your design". I see no obvious topical connection, and if anything, essay writing services exist for quite the opposite reason typically.
Yes, I'm over-analysing this, and yes, I fully support your attempts to gain a little more income. To be honest, the biggest issue I have is the nature of the link - having many friends working in academia, and being white hat typically myself, I have serious ethical issues with essay writing services, and I do think the juxtaposition of that link with your article is rather strange.