I applaud the decision of Google UK to quit running ads for plagiarism and ghostwriting services! It is a disgrace - and the reason I don't use Google Ads on this blog, although we could surely use a bit of income to keep the service running.
As soon as the word plagiarism or dissertation or thesis shows up on a page, Google Ads offer links to ghostwriting services. I disagree that essay-writing services is a legitimate business. Even if they tell their customers not to hand it in as their own work, wink wink nod nod, that is the point of the service and I find it ethically distasteful.
Scholarship is about reading, writing, discovering truth, collaborating - but you do your own work or give credit to whomever did the work you are using. Full stop.
We need to impress on our student's (and, unfortunately, sometimes our colleague's) minds what is acceptable and what is not. That is what will be successful in the long run, as well as looking for alternative methods of assessment.