>felt a little unconfortable asking if it was okay to invoice him for the past >4 weeks of work. Once I got past that I was okay with it....
That was mistake #1. Rule of the thumb, never work for free. The payment may or may not be in the form of money always. Example When you do charity work.

Sometimes you have to be flexible especially if your are new in business and most of your business comes via word of mouth from one client to another. But generally if the client starts defaulting then it shows that the project was not planned correctly and that will lead to his going down sooner or later.

As for puting in the kill feature I tried that once but as you know VFP code can be easily decompiled and source recovered so that does not take you far. If the client is sleezy enough he will bypass it. I have been burnt by that.

The best way is to make a policy of never working for free with one flexibility built in ie to let a client that you "TRUST" delay the payment for a little while but as an exception only.

>.... Any advice for the future when dealing with him.
Don't. There is a lot of work out there it is counter productive to deal with the kind of client you mention.

Mohinder