Always have been. Or at least since the beginning of the world wide web.
Stores had long used the “low price guarantee” slogan to draw customers. And they had trained the average customer to believe that it meant they had the lowest prices. Back in those days price comparisons were hard. Sales ads changed every week or two but other than what was in the ads you had to go from store to store checking the price yourself. Yes, you could call around to different stores, but that was unreliable. Even just getting stores phone numbers was a hassle. Plus, most stores didn’t have their inventory computerized, and the ones that did were only close to correct once a year, right after they did their yearly inventory. So they just had to keep track of a couple of their closest and biggest competitors. If you tried hard enough you could save a few dollars, but it was rare and took a lot of effort. Most people would settle on what they thought was the “best store” and just stick with it. Even when a competitor had a sale at a significantly lower price that was simple enough for them to deal with, they would just pull their stock from the shelves and put a sign on it in the back room that said don’t sell until a certain date. If you shopped somewhere like Sears or circuit City where their sales people worked on commission, You could sometimes develop a relationship with one of the veteran sales people as “your guy”. And they would be able to have this insane knack for “searching the storeroom” for you and “mysteriously” finding the “last box that had been misplaced”.
Then Walmart came on the scene and was a huge pain in the ass by actually having cheaper prices on a lot of things. Enough companies complained that eventually a few suppliers would have a special model number for a few high dollar items that they sold to Walmart and then a different model number for everyone else. But this was only on a few things like computer stuff and car stereos.
And then the internet came along and they were forced to slowly start giving just about every store “unique models”.