The guest who literally carries zero cash ("penniless" in a literal sense), who only carries one payment card which is rejected. The guest doesn't comprehend that they have to contact the card issuer. I have to calm them down and emphasize, please call your card issuer. Sometimes they are dejected or even crying that they can't provide milk for their kids, cat food for their pet, etc.
The guest who only uses smartphone payment such as Samsung Pay, Apple Pay or Google Pay. Their phone payment doesn't work. They get angry, claiming our wi-fi is no good (works fine for everyone else!), claiming their own cell reception is bad in our building (first complaint I've heard today about that), ad nauseum. I ask if they have a physical payment card. They insist they never carry the physical card, and they never, ever carry cash. I shrug my shoulders and with perhaps a kind wink of a not-in-my-teen-years Gen-Xer, suggest they always keep a physical card with them as you cannot totally rely on those smartphone payment systems.
The "guest" (quote marks intended) who makes multiple attempts to get their payment card to work, inserting and swiping, without success, ultimately receiving the Target screen message that they have exceeded the number of attempts and will be denied. Repeat the process with another card, same result. LOD or AP aren't easily reached. We have a growing checkout line while the "guest" gets agitated. Guest has no cash either. I'm not supposed to assume that the cards are stolen and the accounts frozen due to fraud, so I don't say anything about this. Have to suggest to guest that I'll suspend their transaction, they need to call the card issuer and get things straightened out. They leave my area, pretend to make a phone call to somebody, then leave the store and never return.
The guest who only uses cash for payment. Nothing wrong with using cash, but their purchase with tax is $139.99 and they only have $138 in cash and no other method of payment. They have no ATM card to get money from the ATM. They spend three minutes holding up the line "debating" what item in their cart they can do without. A line forms behind the guest. Uggh!
The guest paying with cash but presenting a badly-mutilated $100 bill for buying a $1.39 pack of gum. The bill is obviously torn and cellophane-taped together. It's not clear if the two sides match. Mutilated currency needs to be brought to a bank, they are better at figuring out if this is a legitimate currency unit or if it's questionable. Guest purports to not understand. Arrrggghhh!