Make sure you spell everything out as to returns and conditions (of sale) and shipping and payments you will accepts. Most (I think) don't or can't read too well anyway but if there are issues after the sale you can refer them back to the conditions of the sale they didn't bother to read. Emphasize it's a used item and the photos (no matter how good) will not show every little defect.

You don't want to get victimized by the gotcha game where someone gets the item and goes over it with a 10X loupe and tries to claim defects you didn't disclose.

Once you start selling you will eventually run across a walking horror story.