as opposed to what, though? You don't get a 3% discount for using cash.
In many cases they do actually offer the discount (or tack on the "hidden" fee for using a credit card). In some markets there are also sellers who only accept cash (often discount stores etc.) and correspondingly have lower prices, which is a slightly more inconvenient version of the same thing if you patronize them.
Moreover, we should encourage every retailer to offer this, because getting 2% back (or less) while paying 3% more is not just a net loss, it's also worse for privacy.
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In some areas you do actually, lots of local restaurants for example.