prostitution pays pretty well, if you're attractive.

Attractive, and female. Male prostitutes do get paid a lot less. Also, stress levels and risk levels here are likely pretty high for all genders. If one is in an area where it is legal, possibly less stress and risk, but still likely to be not at all small.

If you can find out and be good at keeping track of the value of collectibles such as magic cards you can make a lot of money buying and selling them.

This seems like an area that's already saturated with a lot of skilled people.