It tastes very good. It is a little bit runny and turns brown after a while. Lots of people make their own jam this way. Except that they use a large pot rather than a frying pan. If you have berries I recommend that you try it. However, it is more expensive than the factory jam.

selling foods in Australia requires food safety certificates (just another barrier)

preserving food generally - yes. People preserve food in many way, and sell it in many ways. Fruit gets dried with ease too. That might be a more viable option.

Do you have an angle on the marketplace that others do not. i.e. strawberry growers, existing jam making companies? I suspect you have no chance to compete... (this is a rational check generally - "are other people poised to have seen this idea first and acted on it". While not always possible to predict; and not always accurate - for simple ideas it can help temper the excitement of shiny new ideas)

When I was a little kid we used to make blackberry jam. You can just pick wild blackberries in some places, which is quite a lot of work, but hey, you're out in nature, it's fun, and it's free. Looking back I think it was mostly my parents picking berries while my sisters and I were running around and playing in the forest and eating half the berries our parents picked.

The recipe for making jam is indeed just berries, water and sugar. We used a large pot though, not a frying pan. Just cook and steer until it's done. Pour the jam into a jar while it's still hot, and screw the lit on. As the jam cools it'll create a slight underpressure in the jar, helping preserve the jam and tightening the lit even further.

Sealed properly it can stay good for a long time. One year we kind of overdid things (my sisters and I were a bit older, and actually starting helping instead of 'helping') and ended up with over 300 jars of blackberry jam. They were still good 10 years later.

Self-made jam tastes much better than store-bought jam. Whether that is because it actually tastes better, or because your brain just thinks it tastes better because you made it yourself, I don't know. But it doesn't matter, the end result is the same.

Pretty sure the sugar is necessary for preserving. You could make it without sugar, but it would just be pulpy juice-water (the sugar is also a thickening agent), and you would have to eat/drink it pretty fast because it will go bad quickly (I would guess a couple days)

I heard strawberry jam can be made with just strawberries, water and sugar on a frying pan on the radio.

I'd use a stove.