That reminds me of a side job I took a couple of decades ago.

A local computer hardware store was offering night classes (9pm to 10pm) for people who wanted to learn about hardware, and I took the job as an instructor for Mondays, Wednesdays and Fridays. Informal agreement, no contract or anything like that. Well, I needed the extra money...

I was supposed to be paid every Friday night, and so it was for the first couple of weeks. The next two weeks after that, I didn't get paid at all and both the manager and the owner was giving me the runaround, they would simply disappear whenever I turned up.

Then the next Monday I did the same and simply didn't turn up. My phone rang 10 minutes after 9pm and it was the owner.

Him: "Did you forget you were supposed to be here tonight?"
Me: "Sure, because you forgot to pay me..."
Him: "Well, come over then, we'll sort this out."
Me: "Will you be there with my money for the past 2 weeks?"

He bangs the phone down, and to this day I'm yet to see the color of that moolah.

Anyway, point of the story is: don't go on threatening that kind of people in any way, it might even turn against you in the end. They know the game better than you do.

Instead, get yourself backed up by a signed contract before you commit to something, and it goes without saying, make sure that the terms are favorable to you, mostly. If they refuse to document the agreement, then you know what kind of people you're dealing with...

Oh, and these days, with Internet at your fingetips, just do a bit of research on your potential employer. Who knows what you might find?