There's a tremendous amount of complexity to the topic, but we'll keep it simple: to maximize revenues, traditional grocery stores historically used the "six week" cycle -- products were offered for sale at a given price for five weeks, then during the sixth week, the price was greatly reduced to clear old inventory and stock new. The "six week" concept is largely obsolete, but the cycle certainly persists (it's just evolved). Manufacturers subsidize sales for a multitude of reasons, and the timing of when their products go on sale (every X weeks, at the end of a quarter, during certain holidays, etc.) is generally consistent. Typically, coupons are issued to sweeten the deals for consumers, and help move maximum inventory. Now, most of us will never memorize these exact cycles, but we should be able to keep track of pricing, know approximately when to expect an item on sale, and at what price we should buy. If you have the income (since some weeks you'll spend less and others more) and pantry space to stock up, you can save big. If you don't, you're better off shopping at Walmart, Target or Aldi.
I spent a year of my undergrad working a co-op with Ralphs (which, at the time, had been acquired by Kroger just a few years earlier), procuring produce. Basically, produce is sold in lots; the price is based upon color, texture, size and taste/quality. Ralphs/Kroger generally purchased the exact same lots as the likes of Whole Foods, except there was an emphasis on local produce (to reduce transportation costs). The primary difference between Kroger and Whole Foods' produce is that the latter is a more labor intensive operation, which ensures that it's handled more properly, ultimately yielding a higher quality product.
Walmart and Aldi, OTOH, do not buy the top-rated lots. Neither does Costco. I'm not a snob, but I can definitely tell the difference. And locally, the Aldi's I've been into are poorly managed. I've seen multiple instances in which product wasn't rotated properly (instead, new product was dumped onto the old product). Obviously that's a big YMMV.
)...
