[eluser]jedd[/eluser]
Really, this is not a technical problem but a legal one. Attempting to solve non-technical problems with technical solutions is an easy trap.
If you are in doubt about your client's ability to pay you, discuss this with your client. If you are in doubt regarding their intent to pay you (a big difference) then you should refer to your contract. Absent a contract you are in especially tricky territory if you go down the path of intentionally damaging their business in an attempt to extort money, or seek revenge. Neither are looked upon favourably by the law, and it would be unfortunate if your legal recourse was jeopardised by your own actions.
