I see. Well I recommend you this:

1. Download a free 3D modeler (Wins3D, Blender) or use 3dsmax if you have it.
2. Import a poser character model to use as a scale reference. Depending on the modeler, you'll have to import it with a scale of 1x100 or 1x1000
3. Import one of this models and scale it so that it looks proportional to the character you imported.
4. Export the scaled model according to the imported scale options (0.01, 0.001)
5. Import into poser.

Or you can scale inside poser, but I find doing so in the modeler faster and easier, as some models can get invisible and almost impossible to handle inside poser if it's too big. You can also use the scale factor option when importing, but it's not very accurate.

One more thing, try turning off Smooth Poligons for the objects and see if they render better. The models from this vendor doesn't  seem to be optimized for poser, but rather for general 3d applications.