I have definitely received larger than 3-4% discounts (5% is pretty common, I've even seen 10%). At the time I had a pretty long discussion about reasons with m

I have definitely received larger than 3-4% discounts (5% is pretty common, I've even seen 10%). At the time I had a pretty long discussion about reasons with my friends, but there's a lot of illegal and legal reasons to prefer cash: (a) you can pay employees quicker since credit cards don't disburse funds immediately, (b) you can pay employees "under the table" i.e. ignoring income taxes, (c) you can pay off your suppliers faster (as above), which is really useful for businesses with poorly documented credit (i.e. receiving net 30 or no credit). Depending on the use of the cash, I could see it being economically valuable to offer even a 15% discount (for illegal use) or 5% (for legal, CC processing + credit reasons).