For me, what works just about every time is the threat of a lien. We send a letter stating in 30 days our attorney will be submitting a lien on the property and that $550 for lien and attorney fees will be added to their balance. I also add in some b.s. that a lien will negatively effect there credit rating. 95% of the time we send these letters, we are far past the state deadline to file a lien. But very few customers know this and they almost always call to pay asap. The few customers who actually know the laws do call our bluff and don't pay, but then all we are out is the cost of the stamp. We send them off to collections.
But when a person gets a letter saying they are getting a $679 lien filed for a $129 blowout, they usually don't want to take a chance.
Why do people not respect us as they do other tradesmen? Because every Tom, Dick, and Harry doesn't think he can be a plumber or electrician!