"The repairs in the long run are actually going to cost them money. They are going to have to do more," he said.
Portside Automotive Services managing director Dan Morris said he, too, had noticed a drop in work but was still managing to get by.
"We've definitely seen a drop in turnover in regards to the amount of warrants being done and repairs. We've been lucky enough that we've been kept busy enough with repair work. I think that feed of repair work will dry up with the warrants.
"I don't think we've felt it yet. I think it will be next year before it's really felt. I think early next year we'll really feel the pinch."
Other mechanics he had spoken to said business was also quiet in comparison to last year.
"Everyone's sort of been grizzling about a downturn," he said.
Mr Morris was wary he might also see a drop in the regularity with which people chose to get their car serviced as many people chose to do it at the same time they got a warrant.
"A lot of people often say I would still like to get it checked every six months but we'll see if that happens. That'll hurt even more if we miss out on the six-month services. That's where the money comes in, it's not in the warrant of fitness, it's in the services."
He also expected cars would need more work when they were brought to a garage.
"Down the track next year when the cars come back in after an extra six months on the road there might be a lot of work needed," he said.
Mr Morris said the price of warrants may go up a couple of dollars but was unlikely to get much more expensive.
Harman Automotive owner Mark Harman said he had also noticed a drop in the number of people booking warrants but said it was not having a big impact on his business.
"There's a downturn in the warrant of fitness sector. All in all, we're really busy at the moment. We have had some quiet periods. I don't know if it's because of that or not."
Mr Harman said his company's service had always been tailored as a once-a-year service so the change was unlikely to make too much difference.
The changes
• As of July 1, 2014, vehicles first registered anywhere in the world on or after January 1, 2000, will only require a warrant of fitness once a year for the lifetime of the vehicle.
• For new vehicles, after an initial inspection, another warrant inspection is not required until the third anniversary of its first registration.
• Cars registered before January 1, 2000, need to be inspected every six months.