Product problem
http://www.daz3d.com/tears-hd-plentiful-tears
When I "use" the tears they don't appear in the scene. The model's eyes look a little shinier but that's all that happens, no tears on the face, nothing appears in the scene tab.
Can anyone tell me if there's a problem with the product? Or am I just using it wrong?

Comments
First question, Have you actually applied any of the morph dials?
Parameters tab>Pose controls>Head>Expressions>Tears HD
you should see something when you change the dial settings in the viewport.
Be sure to use the correct version of the material presets, 3delight for that renderer, iray for iray.
That appears to be all that those presets are is shader presets.