The answer to the
OP's main question is relatively straightforward:
The mass of the trailer and cargo must be within the specified tow capacity of the towing vehicle and hitch. Where there is no specification, it must not exceed 1.5 times the empty mass of the tow vehicle. (WA law)
So, for example, your average BA Falcon, fitted with HD hitch, weighs around 1,500kg, but can tow 2,300kg. Which yes, is approximately 1.5 x
So providing your trailer weighs less than around 750kg, a BA could tow a BA.
How much does a trailer weigh?
Interestingly I would have estimated around 6~800kg, but I don't actually know.
In WA, where you are more likely to come unstuck is that most hire trailers will be limited to 2,000kg GTM. (Over that requires remote-controlled brakes.)
As to whether its safe, that depends on the condition of the tow vehicle, the condition of the trailer, weather and road conditions, the care and skill of the driver, and the balance of the load.
I've done it, with great care and moderate speed, on good roads and freeway.
One way to look at it, is that any problem is going to be multiplied threefold or worse. I wouldn't do it in the wet, or on gravel. I keep the speed down, leave massive gaps for braking, and take corners at a snails pace.