I will never do consulting again for a former employee unless I get paid upfront. A previous employer "adjusted" an incredibly reasonable bill. Then two months later their nginx server goes down and he calls me in a panic. I required them to deliver the check before I even took a look at it. Out of spite I charged him a near egregious amount because of that. On the plus side the office manager had a grin on her face, she forced the owner to pay the full amount of the previous bill. She thought it was incredibly underhanded.