Here, those charges normally hit our debit cards - not the account itself in the sense that a direct debit skips the card and basically functions like a check/cheque.

Nothing on the card, it declines, they can't charge.

We used to use EFT with our ancient transfer system, still do for direct deposit payroll and such, but otherwise it's all cards here. Very few people use account transfers. so none of that is a risk here. It takes two or three business days, and the merchant has zero visibility into whether or not the transaction will actually approve at the time they make the sale. Online merchants wouldn't send items without cleared payment, but very few even use those transfers anymore because there's just no information on whether the customer actually has the money or not.

In the airline example, they never would have gotten their money unless they were ok with making a very big problem out of it - most companies wouldn't, and most companies would not pursue someone who owed them some nominal amount.

Credit cards don't work like that here, they approve whether you want them to or not unless they're locked, but debit cards lend themselves to sequestering money like that in multiple accts.