Only sell clothing that is in very good condition.
If an item has any faults what so ever, describe them in your listing, it is better to be honest.
If you have any items that are in poor condition, give them to charity.
Be honest about postage costs, and if something is heavy and the postage is high say so in your listing.
Describe the item as best you can giving, measurement in inches for trousers etc.
Give buyers confidence, by writing an about me page, describing your service levels.