I have worked for equipment dealers 12+ years of my career, primarily as a mechanic, but I have been in charge of parts, ran the shop, and even sold a couple of tractors. First come, first serve in a perfect world is how I run things too, but it doesn't work in every case. The guy that just plopped $80K down last week for a tractor and has a problem, is going to get pushed ahead, so is the contractor that has bought a dozen tractors from you that has an emergency. The sales department drives the business, they will ultimately dictate who comes first.
Many equipment dealers consider the service department as a necessary evil, and few are actually a profitable part of the business. The last dealer I worked for had a service manager whose standard reply to a customer was that it would be 3 weeks until we could look at their machine. One of the last years I worked there, another mechanic and I ran the shop without a service manager. Our response was to have the customer bring it in and have us take a look at it. I usually triaged it in a couple of days, got a price to the customer and ordered parts. It wasn't uncommon for me to have 5 machines apart waiting for parts. Parts availability becomes part of the decision making process along with overall customer attitude. How quickly a customer pays and how much you have to hold their hand after giving them a bill plays a part too. If the owner walks through the shop and comments on how it takes so and so 90 days to pay, it will affect the priority list too. Anyway back to my point. The year that we ran the shop, was the only year out of the 20 he had been in business, that the shop actually made him money. We were about repairing as much equipment we could as fast as we could.
When it comes to warranty the tractor business is not like the automotive business. I'd say in most cases you are lucky to get 80% of the time you put into a repair. I was pretty good at writing Kubota warranty claims, but it would take an hour to write a claim that would get you paid for all of your time if there was any complexity to the repair at all. Short Lines are even worse. I made a repair on a machine one time when my shop rate was $75/hr and all the manufacturer would pay is $40/hr and then only paid 4 of the 6 hours I had into the repair.
Brian