I worked at a fast food place where our power went out. They forced us to keep ... open and selling anyway. The 240v was out so no grill, but 120 outlets worked so we could make coffee/tea. That was about it. Cash registers didn't work. I was writing everything by hand, calculating tax, etc, keeping records.

2 hrs later, the regional manager - WHO HAD TOLD US IN NO UNCERTAIN TERMS THAT WE HAD TO REMAIN OPEN DESPITE NOT HAVING POWER - came in and chastised me for 1) not wearing the full uniform (we had no AC and it was July, so I took off the tie) and 2) handling money without a register. "You can't guarantee your numbers are right - that's what computers are for". "But... they're down, and you said to stay open and keep selling". "That doesn't change the fact that you might be making mistakes!"

Insanity.

Dealing with cash is complicated actually. You need to protect it from theft. You need to count it daily. You need a bank to deposit it. You need to have change because people don't bring exact amounts. Having change requires a bank or some other facility to exchange currency with.

Cards require a machine, some kind of network connectivity, and an account. It's actually a lot easier to deal with as a small business. Most of the people I know who go to conventions as vendors prefer cards because it greatly simplifies their logistics.

Yes, but I was talking about a scenario where there is no network connectivity and hence no ability to take card payments.

In the case of getting paid something versus getting paid nothing, I am guessing most merchants will opt to put in the work to accept cash rather than shut down.

Note that some retailers can and do store and forward transactions, for example with gas stations using satellite connectivity for payment processing. The amount one stores depends upon one's fraud tolerance.

There are attacks where bad guys will disable a gas station's dish (by covering it with foil among other methods) and then rack up a bunch of gasoline sales with a stolen card. They've got generally got a limited window so they have to hit a bunch of local stations quickly, but meth users aren't known for high dollar scores.

But if someone robs you then you have both zero money and less merch due to sales that day. I'm guessing a lot of places will err on the side of caution rather than some income.

I saw a supermarket operate with calculators ~10 years ago when power grid was off for days. I don't believe I will see it again at least not in any big store as financial conciliation is a PITA and the old ways are lost. But small vendors that are often marginalized by the market will.