All Mark has to do is reduce his price a little.
People will then rationalise their decision to buy Mark's honey by telling themselves that if the price was the same they'd buy Barry's because they care about the bees.
Of course it is also up to you. You can always choose to buy from dodgy sellers to save a few bucks.
Brands exist for a reason, to guarantee a certain quality.
Also poverty (lack of options). Think of how the 70% of the population who barely gets by would read your comment on being cheap.
Don't know about the US, but I think most people there shop at Walmart or Costco. Seems to work fine.