The mistake was in allowing the headstone to be carved and put in place before it was paid in full. You aren’t required to order an expensive headstone or, indeed, to put a headstone on the grave immediately. The cemetery will provide a temporary headstone. Some people take years to emplace the permanent headstone. If they couldn’t afford the headstone, why did they order it?
What’s the difference between placing something and emplacing something?
perhaps the stone cutter was being nice and the niceness was repayed with non-payment.