That's fine BBB, but it doesn't cover services. Small shops can't make enough money just selling PCs and random bits of hardware, they have to provide paid services to customers.
For a business customer, this may well be onsite. So if you repair and rebuild a server, say, there could easily be a multi-thousand dollar bill attached to that, and most businesses aren't expecting to pay you on the spot, assuming you are able to somehow give them an invoice then and there.
There's also the problems associated with people paying by check.
Also, if you think a shop can easily fit all their purchases on a credit card, you obviously don't understand much about small business and cash flow (no offense intended).
I can't afford to help CougTek right now, but there may be others here who can offer tangible help and, once this crisis is past, advice. There may well be no future in his business model - you don't need to look any further than Tannin.