Too few of us have the confidence it takes to risk irritating a customer by
stopping work or withholding further shipments, or whatever it takes to get
someone's attention. As for mechanics liens, they can be very effective in
certain states if the property owner is more substantial than a paper shell
designed to shield him from creditors. 

I've never regretted any decision - however hard it seemed at the time - to
stop and insist on payment before proceeding. The only ones who scream are
the ones who were planning on cheating you in the first place.

Mike Edison