I know someone to whom this happened. But this isn't a Walmart thing - it's a universal thing. With the destruction of local and regional chains, national price competition finally became a universal phenomenon. I am personally acquainted with someone who once operated a mom-and-pop grocery. There was no way she could compete with any large scale player. Big players have higher turnover and can dictate prices to the vendor. Mom-and-pop stores have inventory that sits for a while and definitely cannot dictate prices to their suppliers.
I also personally know someone who was a domestically-based Walmart supplier, and went out of business when he couldn't meet the price they demanded, and did not want to take the trouble to move his business abroad. It's the way of the world, and not a Walmart-specific phenomenon. Walmart is just bigger, so it touches more people.
Didn’t say it was solely Walmart, just that it began there.