the question is just like the Title.

you mean how to apply?
Look at news section and look how to apply

is the market squad member get paid?

No they don't get paid.

so, what is the benefit of that?

They help the community, keep order in the market, moderate the market boards...

They don't need to have something in return to help out.

oh, I see. thx

Well they have the fun of banning and infracting.

No staff position pays you (except for a few higher ups) and you should not apply if you are looking for payment.

Is the Non-Existing is banned?