"is not quite a significant part of the Thai moneyboy scene strictly - from a purely legal viewpoint - made up of criminals"
Yes, including farang who hire the prostitites.
I thought the OP was an April Fool's joke, but apparently it isn't.
Sorry, abidismaili, but i think your post is a bit silly. What foreigner would take a guy to court over a money matter when it would be obvious to a judge that the money probably involved prostitution? The farang would basically be admitting he had broken the law.
Thai guys lie to us all the time and they all seem to tell the exact same lies. Any mention of a sick mother, dead buffalo, friend in hospital, sister involved in a car accident etc, etc - should set off the alarm bells.
The simple answer is not to give them any money. The answer you'd get from a judge is one you wouldn't want to hear.