Avoid liquid margarine or cooking oil for cookie baking, unless the recipe calls for them. Bake on the middle oven rack for even baking. Remove cookies from cookie sheets immediately unless otherwise directed in the recipe. Cool cookies before stacking or storing. Also chewy bars do well.
Bar cookies hold up best if sent uncut inside disposable aluminum trays.
For an idea of how brutal shipping can be, pack a dozen cookies, put them in a car trunk and drive around with them for a week. For individual cookies, wrap each in plastic wrap. Then package all of the cookies in an airtight container. Pack containers into a strong box. Do not use string or twine on your package.