"F*ck you, pay me"[1]
In which Mike's lawyer makes the very good point that you should really put an attorney's fees provision in your contracts so that the purchaser pays your legal fees if you need to chase!
In the end they paid 2 weeks after the net-60 expired. Probably calculated to be maximally annoying with the least amount of risk of legal costs. Really takes the wind out of you. Selling to California startup type companies is so much nicer, I once took a call, negotiated a whole new pricing model closed the deal, entered the product details into FastSpring and the customer paid 40k for the yearly subscription on that model that same afternoon.
I tend to disagree with that mentality.