Yeah, although the exact late fee was not specified very clearly. I did get paid a retainer up front, what is not happening promptly is the final installment, it looks like it will occur after our original agreement. I should think about getting the final payment before making the site live, although there are usually tweaks needed post launch, and I host my sites on my own server anyway, so I have some leverage. I just need to better refine how to utilize my powers fairly and perhaps redefine payment policy.
I hate chasing people to pay, that's easily the one thing I miss about a 9 to 5 job!