One of my friendly competitors (in my business, all of my true competitors are pretty good people!) came up with a suggestion that I'm going to try out.
I had posted (on another forum) that one of the problems that I face in marketing violins on the internet is that these instruments are much easier to sell in person because I can play it, and the prospective customer can tell what it sounds like. That is pretty hard over the internet.
My competitor told me that he will invite a prospect to call him on the phone, and play a selection of instruments over the phone. While the fidelity of phone transmission doesn't really do justice to the tone of a violin, this approach accomplishes two remarkable things.
First, the potential buyer gets a preliminary idea of how the violin sounds when played by a professional.
Second, and this is a biggie, it proves that the instrument is properly set up and actually playable.
Most of the volume sellers of violins on ebay have no clue about what they are selling, and wouldn't know where to start in order to actually demo their instruments. For starters, the volume sellers usually ship instruments that are not even in playable condition -- to customers who don't have the background needed to properly set one up.
I find this idea especially appealing because it fits in with the general principal that success on ebay involves personal added value. (I just wish I had thought of it myself...)