In my experience of both British (very serious guys & leeches) & European (only slightly less so), if it is being shipped & they can work out,or even suspect, how much it is worth, they will have their pound of your flesh. An American friend sent a baby's rattle, skillfully hand-carved by his good self recently. Her Majesty's Revenue & Customs want £30/€35/$44 for it, meaning they think it is worth what...? It is a present to an as yet unborn child for goodness sake. I really dislike my so called government at the moment.

IMHO Having your friend bring it over as described sounds like the best bet. Guitar smuggling is so low down the list of priorities that it is not worth worrying about.