I've claimed via small claims before though not for lost items. A few years ago, a high street developers 'boiled' my slides from a trip to the Alps. They tried the compo to the value of materials trick which I rejected. I got Fuji to write an experts report and the Defendant paid my claim (inc expenses etc ~£600) on the doorstep of the Court.
I wouldn't hesitate to take the seller to Small Claims it's very, very straightforward. Your claim is not for £50, you need to add your time, buggeration etc and make it several £100's. Sod em.