The worst part about selling on Ebay is the bad buyers. The only times I've posted negative feedback is when someone bids and wins, but never pays and never responds to e-mails and never informs the seller that they changed their minds.
My advice... start out slow with only an item or 2. Also, you should try to state a day of the week that you ship. Otherwise, the buyer might expect you to ship as soon as payment is received. For instance, if I'm selling during the holidays, I state that I only ship on Wednesday's (since I usually take those days off to go shopping to avoid the crowds.) If I sell during the summer, I say that I only ship on Friday's since we have summer hours and only work 1/2 a day. That way if someone pays on a Monday during the summer, they know that I won't ship until Friday. If I do have time to ship before then, they just think it's great that I did it earlier.
Also, make sure that you mention that shipmens are held until the check clears the bank. ...and Make sure it clears by going online to your bank account. I've shipped early and had to chase after people for the payment and the bank charges.