The people who try to be machmir on this generally have no idea what they are talking about.
The majority of the chometz that is in your typical local jewish grocery store, was purchased from a jewish distributor. Hence, the entire stock is a problem of chometz shavar alav hapesach until at least the summer. All dry goods from heimeshe brands could have been in the distributor’s warehouse until the winter. There is some chometz that is not even fully rotated until several years. The kosher food economy is self reliant. The further one goes from the kosher retailer, the less of an overview there is on all matters of the supply train. There isn’tmuch certainty who all owned all the chometz that is currently in Wal-Mart.
There is no reason for the local kosher grocery to mark what he brought in after pesach, because that was also owned by a Yid befor Pesach and was sold to a Goy. The grocer has no way of knowing where and when to draw the line on what was sold over Pesach. The same goes for the distributor. It would be very costly to keep track of it. And you Mr. Machmir has not offered to pay for it. I have news for you. Wal-Mart is not tracking this either. Nobody really is. There is a basic awareness of the national distiributing network and one major distributor and several smaller ones are known to be problematic. Nobody is watching if one of the smaller jewish distributors sellsout to a nonjew. This applies equally to chometz that was or wasn’t sold. When we shop by a Jewish Grocery there the knoweldge that they are largely working within the network and all their chometz was properly sold. There is no such assumption with buying from nonjews. I’m not saying it’s a problem, but it is definitely not a chumrah to use an unkown venue in place of the entire kosher food network.
I assume that all post pesach bread is from flour that may have been sold. Do you buy your bread from Wal-Mart for a month? Do you avoid bread crumbs in all jewish resturants all year? Hard alchohol? Beer that is served by a local simcha?
This is not chumros. It is not even hpocrisy. It’s ignorance. Such people have no idea how kosher food works and are a hindarance to enabling kosher food.