Clarence to answer your question you should not be charged customs tax if Beckett remember to mark the form as returned goods.
I did a large submission for the site a few years back that was of a high value and there was no customs tax because Beckett said they were returned goods.
If they don't just keep the records of what you send out and show this to customs and you should be alright. At least this is what customs told me at the time.