"for which I was paid one gravis ultrasound ACE. I think I ended up better on the deal than the owner, but it was a close-run thing. ... Another time I was contracted to do a job for an oil company. It took me a month to do something that would now take me a day, and the end result was so bad that they got no return on investment of the the AUD 300 they paid me for the job."
You're undervaluing yourself.
Even if you did absolutely zero work that doesn't mean the company that "hired" you got zero value out of you.
They probably got some social benefits from having you around, making the place you worked at less lonely, and perhaps making some people at the company feel better about themselves for hiring an intern or gave them an opportunity to teach (which can help the teacher as well as the student). You probably also gave the other employees ideas and feedback, and may have tested some of the work they did (essentially acting as part of QA).
All of that is worth more than a cheap sound card or 300 AUD.
You're undervaluing yourself.
Even if you did absolutely zero work that doesn't mean the company that "hired" you got zero value out of you.
They probably got some social benefits from having you around, making the place you worked at less lonely, and perhaps making some people at the company feel better about themselves for hiring an intern or gave them an opportunity to teach (which can help the teacher as well as the student). You probably also gave the other employees ideas and feedback, and may have tested some of the work they did (essentially acting as part of QA).
All of that is worth more than a cheap sound card or 300 AUD.