Somewhere on your webshop or website you should address shipping instructions
such as: costs, what if not home, what to do if wrong size, return instructions,...
Basically all the questions that you'd ask yourself when ordering from a new site, explain them on yours. There is no such thing as too much information.
Brainstorm, ask your colleagues, friends, family, get information from anywhere you can. Everybody ordered a package atleast one time in their life.