Hello,
I bought a Sonata 16 inch viola from Stringers in London a couple of years ago and started lessons with a wonderful teacher. It sounds lovely, but unfortunately my ancient left wrist just would not bend round far enough to be able to play it ... I was going to trade in for a cello, but have now decided I should focus on piano (my main instrument) full-time. When I bought it Stringers said they would buy it back if I wanted to sell it, but they now tell me they won't (it's a different person running the shop). I've just been advising on selling pianos on the Piano forum, but have no idea about selling a viola. What would forum members suggest -- online sites any good?, music school notice boards, teachers, auctions ...? Thanks for your advice.

I would ask your teacher if they have any pupils looking for an instrument. My violin teacher buys up violins that he thinks might be suitable for a pupil in the future (eg child moving to 4/4), that way he can normally provide something. He also keeps an eye/ear out for possible instruments if someone asks about up grading. So maybe your teacher will know someone on the lookout for new kit.
I gather that second hand (bought from new) instruments are like new cars - big price drop, but perhaps more experienced players could confirm that.

Cheap instruments drop in value quite quickly but good quality instruments should hold their value.

For example a Stentor Conservatoire will not hold its value, you would probably get about ?120 for it 2nd hand but it retails for ?195 - ?225.

However a Stradavarious violin will never drop in value.

Maybe put an ad on gumtree.com or in you local paper, put a ntoice on your church/library noticeboards and see what happens.