Hi, there is a 'reasonable' re-sale for well looked after monsters in most of the UK - but never during the winter. If selling - bset to think about it at the end of March or early April, so - to get a good deal when buying, best to try in the late autumn - late October.
There are quite a few dealers in & around London, though not all are to be recommended - for either pricing or quality of servicing. There are also soem that do a very good job, but are not authorised dealers - which is ok if the bike is no longer in warranty.
Can supply more info if you wish - do email me - ck@ukmonster.co.uk
Tell your brother - best of luck - and to join the UKMOC while he is over here - we have lots of meets etc, and members near to where he lives could possibly help out.
CK
www.ukmonster.co.uk