How does the client make money?
There are really two main ways your client makes money from your Selling Assistant service. If you’re just buying your client’s items outright to resell, you’ve already paid your client that flat rate, so that’s already taken care of. If you’re charging a fee or commission, however, you’ll most likely be paying your client the actual value their items sold for less any expenses.
Just as you were probably most focused on how you’d earn money from your service, this is the aspect that your client is the most concerned with. Otherwise reasonable people tend to become much more paranoid, impatient, and… well… crazed when money is involved. It’s your responsibility to make sure that you handle all these money issues professionally and in strict accordance with the terms you outlined upfront to give your clients confidence in your abilities and trust that you won’t swindle them.