I've been investing in stocks ever since my first job. I've done reasonably well, and I focus on companies that focus on making their customers happy - and they do better than average long term. That's great salesmanship.
Only bread, cheese and processed products in original packaging, so I guess this proves your point. But they are doing fine to this day, because there's only so many people you could tell (for various personal reasons I didn't want to pursue anything serious, like ratting them out to safety inspectors and hoping they didn't bribe the local inspector, like a certain bookstore I know of... but that's another story), and people tend to stick to their local grocery stores anyway (price and location sensitivity).
For what it's worth, despite that I'm now distrusting businesses by default, I try to compensate for that; if there's a store or service provider that I feel treats me fairly, and I don't see any obvious signs of deception in their overall business practices, I tend to stick to them despite cheaper options available. I feel fair business should be rewarded, and I do my best to put my money where my mouth is in this area.
Before I moved to a smaller town, there was a grocery store I bought regularly from due to optimal location and relatively middle-level prices. I was pretty sociable back then, and befriended some employees. This eventually led to them warning me about buying meat on certain days - turns out, they were forced to wash stale meat with detergent to erase the bad smell, and sell it as fresh. I recently confirmed it with one of the ex-employees, turns out their manager actually opposed that, but this was forced by the higher ups in the management of the whole shop chain.
That, and bunch of other stories (some second-hand, some first-hand), essentially ruined my trust in regular small business.