Although I've never done it internationally, I frequently have used UPS and FedEx to ship luggage to and from vacations. In terms of customs, all shippers have forms that you have to fill out when shipping internationally on which you indicate the contents of the package and their value. This should be all that is needed to get the package through customs (although if you are shipping clothes home, I would be sure to indicate on the form that the package contains used clothes; this should help avoid any issues as to whether a duty or customs tax is payable).