just say, "i bought this Monitor, i opened it, and its not the right 1, so i rung the trading standards office, and they say, by UK law, i'm allowed to return it within 14 days", he'll then say either ok or no way, then you say "i was also told to tell you, that not accepting this also means that your breaching trading laws within the UK and are liable because of this" if he don't give in, ask to speak to there manager, tell him, but kiss his arse, "i know you'll be able to help me sir"etc, but by UK law, you are in your rights to return it and get a full refund.