Just happened with my dad, with one of his rental tenants. One of them lost his job (didn't get the job after the probation period), so he had booked a flight back home. Except because of the war in the Middle East, the flights were delayed constantly so he couldn't go back - and given that his flight was on a budget airline, it would take ages until normal operations resume (they still haven't resumed). The guy kept telling my father that he would pay once his ticket was booked, up until the very last minute when he revealed that he was broke and could not pay, burnt bridges and all. He incurred a significant expense after booking a flight with a non-discount carrier airline.

The irony was that had he revealed that he was broke from the start, my father wouldn't have minded as much about the rent (he has forgiven rent in such cases in far too many situations), but would have also helped him get the ticket for cheap.