Perhaps this person has fallen on hard times or dealing with something you dont know about like being a carer for a parent or similar which is why they are short on money?
Plenty of people are hard up for any number of reasons. Such people don’t tend to keep organising expensive nights out, though. Even the scammers who hang around town centres approaching passers-by and claiming that they don’t have their bus or train fare to get home don’t try asking you for enough money to hire a limo.
IIRC the CF friend ended up having to ring her parents to do a bank transfer so that she could pay her bill!
I don’t know which thread it was originally on, but IIRC, I’m pretty sure she was already something like £250 into an unauthorised overdraft, meaning that any money paid into the account would instantly go against paying that off; hence £260 would need to be paid into her account before she’d be able to access a tenner. I think her parents had to pay something in that region into her account, for the sake of buying a drink or cheap lunch that she’d just assumed she’d be able to grift her –target— friend for, to avoid the café/restaurant quite legitimately calling the police out to their daughter the thief.
I LOVE the tap water idea- so much more subtle –and PA— than refusing a drink outright. She can’t hurl any allegations of ‘unfair’ at you for excluding her from having a drink, as she has a perfectly good drink (would suit me just fine as I always have a soda water anyway 
) – she would just have been able to have had a more expensive one if she’d had the money to afford one, same as with anything in life.
The ‘saving coins’ excuse is a mighty brazen one, though! It’s just one tiny little step from saying “I prefer it if you spend your money to buy things for me so that I can keep mine for something else."
Like a previous PP, I might keep a non-standard or commemorative 50p or £2, but I do that instead of spending it. If I have to spend it or want something more than I want to keep the coin, it gets spent. Plenty of people find it helpful to budget or save for something (or for charity) by putting by every coin of a particular denomination that they receive instead of spending them.
At no point would it ever enter my head that I could both keep the coin but also have goods to its value by expecting somebody else to use their money on buying it for me.