Tanks selling their bodies to Rogues/Ninjas...

[Yukiko]

No one is forcing money out of anyones pockets. These are agreed terms by both parties. Who is being wronged?

You are using the need of someone else, thats not the same as agreeing with their free will.
While it is true that you are not holding the gun, you make use of their predicament.

Its like sending e-mail spam with telling them to pay money: someone is paying and you made profit...
why do you think this is rendered illegal in real life? snowball effect
Same as selling trash to old ladys: oh sorry they are paying me - its their free will to pay me!

Edit:
Example: A static of 8 players where the 8th cant be online at that day - getting the 8th random and let him/her pay.
The random helps the static to even get into the dungeon, so it is a win-win for both, to add payment it means to exploit the situation!
You dont even give him/her any kind of service, you get paid for something you dont have to do anything...