I thought if you were running a business, you could claim for as many cars, trucks, tractors etc as you used in the business.
BUT,
if any of them are used for private purposes then you have to keep a log book to prove percentage of business use.
If you push the limits such as by claiming 50% business use for your trail bike, they will push back and demand bags of proof on everything.
So, be content with what's reasonable and don't make a welter of it.
Also, to claim a vehicle as a business expense, it has to be registered as a business vehicle, not a family vehicle.
I don't know if NSW makes that distinction but WA does.
You cannot register a car as only for family use (cheaper license) and then claim it as a tax deduction.
Your accountant might be giving you that line because he doesn't want to get caught up in trying to justify your bovine excrement story when the tax man comes knocking.
It doesn't look good on his plate when he is shown to have accepted something which is obviously wrong.
Anyways,.. you can always ask the tax office on what the rules are.