Listing is working :
When working for others you should get paid. But when listing for others you have many things to take into consideration as ;
1. how much do you expect to earn per listing ?
2. Do you want a flat monthly fee or a commission ?
3. How many listings will you do for a flat rate ?
4. How will the customer profit, what with listing fees, selling fees, paypal fees & your fees.
5. Will you be pricing the items or will you have them price the items before you list them?
6. Do you want to do the shipping or do you expect them to do the shipping.
I personally tell the client that : I list the items for you. It is your responsibility to watch for sales, and to ship out the items as I do not have storage for your items. I tell them to put a price on each item. Then I can't be blamed for selling something below what they believe the value is.
I prefer that i get paid through PayPal or cash rather than check, or money order.
With people I don't know I figure my fees & get a deposit in my PP account before I'll begin listing. I will not promise to list more than 3 items per day or 15 items per 5 day work week.
You will need to make your self heard & make sure they agree to your terms. A signed contract is best. Make sure you have the time to keep your end of the contract.
I hope this helps you decide if this is what you want to do.