Only envelopes go missing now...

Well,, on one of my ID's I sell CD's and DVD's, not big earners but good bread and butter sales. These seem to be the only things that go astray. Parcels seem to always get there but not items sent with stamps(no tracking), one in 10 vanish. Dishonest buyers or light-fingered posties or both? One recently filed a claim 2 days after payment and Ebay refunded after 16 calendar days. Annoying.