More accurately, a 3.75% discount if paying in cash. Merchant fees are not to be ignored. We ALL pay them, with a good bump in the last many years to "cover" the costs of the reward cards we all try to use. Then there is the cost of dealing with card user issues, which is now 100% DIRECTLY funded by the merchants. When someone questions a charge, the merchant has to "pay to play", so even for a $200 ticket, it is likely cheaper to accept the refund (which we all pay for in increased costs).
If your clients provide a GL, look at the rate their CC fees actually are (assuming accurate entry). Processors sell on the as low as 1.99% theme, but the reality is, for most small businesses, getting an annual actual cost even near 3% is the exception.