There's definitely a large set of sites that should not have a viable choice, not from Google and not from anyone else, as we-the-users want our distribution channels to filter out various groups of SEO spam.
The only question is whether this site is one of these or not - and even if it's not, a certain number of 'false positives' is acceptable and less strict filters definitely are not. If you're running a site that's skirting the line between spam and not-spam, then either you take on the risk that you might be dropped by google and others, or (perhaps preferably) stop doing that thing and do something substantially different.
The point I'm making is that if his business is only possible because of Google, it's silly to ask what his alternatives are.
It's not like he'd have a thriving business if only Google didn't exist. Instead, he's reliant on Google choosing to rank his page highly enough to get traffic for search queries that will result in people clicking on his affiliate links (who he's also reliant on). Google doesn't owe him any particular ranking. If people search for his example "cheap portable generator", does Google have some ethical responsibility to put his site at the top? Or even on the first page? Or to never change where they rank it once it reaches the first page?
What does that have to do with it? If other search engines were more popular, would that change this situation? Maybe there'd be a handful of algorithms to arbitrarily rank him instead of just one, but the dynamic would still be the same. He'd still only be in business as long as their algorithms happened to think his website was slightly more relevant for "cheap portable generators" than other websites.
What other viable choices does this site have aside from Google?