that quote comes across as one taking advantage of another over a technicality. the whole story smacks of sharp practice, if not a bit melodramatic, our hero gets the shop closed down and two dangerous wrench wielding menaces to society get sent to jail on outstanding warrants. back to the opening lines. without initially knowing more it's easy to see the conflict from varying points of view and to draw very different conclusions. I would have negotiated (maybe the protagonist did negotiate but called it arguing) with the owner if he did indeed perform work. calling the guy scum only because he's a foreigner is pretty stupid also. as for me I doubt I would call the police, flip the guy off and drive away laughing.
I had some work done on a truck and was quoted a sum. when I went to pick the truck up they wanted to charge me x2. I asked the girl why qoute one figure then bill twice as much. her boss (a young guy) comes out immediately, sweating big drops because I also had not signed a work order. he explained that the girl had misqouted me over the phone, produced all the replaced parts, lifted the truck, showed me all the new shiny parts that were installed and so forth. I was satisfied with the answer and paid up. as I was paying up the owner who was listening in the back gave me a 25% discount. that was ten+ years ago, today I have a great friend who is also my vehicle's maintenance provider. that's the only place we take our trucks and personal vehicles. all over a potentially ugly dispute which was handled very well by the shop. it helped that they were dealing with a reasonable customer though.