photos, (in listing and on item page)
generous descriptions (lots of information),
honesty,
low starting bid plus a ‘buy it now’ price (shoppers in a hurry will not look at auctions),
reasonable postage charges,
offer pick-up,
generous, courteous answers to questions - post in the page of the item you are selling

be honest, take LOTS of pictures, work through PayPal. I know I will not even CONCIDER buying from a seller who doesn’t use PayPal.