Still leaves them with a 50% discount until you take 'em to court.

Half up front is a bad model. A better model is 25% staged throughout a project, with 25% post completion. This means that they don't get live unless you've at least 75% of the balance paid, and you then operate a one month warranty period at the end of which they pay the balance.

With these particular goons, we have our 75%, and a never-ending stream of "we've re-interpreted the specification and believe that X means Y, Z, Q, R, P and M, which we require before we will sign off", much as we'd anticipated.

This is why we charge a minimum of 75% prior to go-live. Means that even if they do decline to pay the remainder, we aren't left out of pocket, and can play silly buggers for as long as it takes for them to get bored and go away.