Both your examples mention single digits hours, ie very small amount of money.
The problems tend to happen if there's larger amounts of money involved. So it's important as a contractor not to enable a situation where they owe you a lot of money, especially if you have no leverage.
Yup, but make sure they can sell the product, not sell you.
Also, never give up control of the finances - abdicating that responsibility means you will probably get screwed. You need to be technical about ensuring your efforts are not stolen.