More things to consider before selling for clients on Ebay:
Left Items: What happens when items do not sell? Will the client pick up the items or will the client just leave them for you to deal with? You need a policy in your contract that states any item left for a certain number of days becomes your property. Point this out and have the client sign it. I had a problem with this when a client left items in my home for six months. I did not feel I could dispose of the items because they did not belong to me. Finally, the client got in touch with me and accused me of stealing. That was the last time I sold for anyone.
Records: Keep detailed records of the clients items, how much they sold on Ebay, Ebay fees and how much profit both you made. My records made the woman who accused me of stealing feel very foolish.
Clients: Can you deal with all personality types? Can you handle a customer that refused to believe her dollar store item will not sell on Ebay for hundreds of dollars? Are you responsible enough to get items listed right away and stay in touch with a client? Will you respond quickly to their questions, concerns or demands? You are providing a service so you will be expected to serve in an appropriate manner. Sadly, enough the definition of what is appropriate may change from client to client.
Profit: Many who sell for others will only sell items worth a certain amount. After all, it is not worth your time and effort to sell a $5.00 item when you may only make a few dollars. Do not fool yourself into thinking that selling hundred $5.00 items for one client will be worth it. Trust me, it is not worth your time. Decide how much money you want to make off of each item and only sell items that promise to be worth that amount. Many clients will expect you to list items at least twice before giving the item back so that doubles your work for a low ticket item.
Contract: Never do business with clients without an agreement. Make sure you set your terms and verbally point out each term to your client. Also be sure to have your client sign the contract. This will prevent many headaches for you if something goes wrong.