Depends on the site. If its a small/medium business, every LLM is now looking for "reputation signals" and "authority signals". This means everything from your basic SEO on the site with incoming links, how updated your google business profile is, how many reviews you have, how recent they are. They're also looking at any kind of references from other blogs, substacks, youtube videos, social media shares as well as a number of other things they look for.

I would imagine in smaller industries, flooding the internet with fake information, then linking it all together would be somewhat easier - but it still takes quite a bit of work to get even just the major LLM's to give the consistent responses you want to see.

You can't count on that, but quantity increases visibility don't it, and it takes a single prompt to spit it all out. Couple that with social media bots and you've got a decent modern and super cheap propaganda machine. Now imagine you toss millions of dollars at that idea.