How?

[Aviva]

Why would he offer you 50 dollars to write up the method?

How do we know that he's not actually using aforementioned method?

Why do magicians care about catching other magicians out?

copied from the video information:

Be sure that your tutorial is detailed enough to reproduce the routine. If you can reproduce it but in a different way which still is safe and similar, you will still get $50. The 26 other owners of this routine's method can backup the replies at anytime.

and why we like to figure it out is because its not a challenge for nothing.