Besides possible fake 'credibility' boosts this may impact your Edgerank etc. thus acting like social media SEO booster. I think some external services evaluate their rankings on number of likes as well.
"But if your visiting an online store and you see a lot of likes under the product then this might cloud your judgement ;)"
I give it 12-24 months before the DoJ/FTC deem Facebook `Likes` illegal under antitrust law, for the exact logic you just laid out. It's a clear antitrust violation because it's a way for firms to mislead customers about the quality of their product.