Check if smoothing is on in your render settings, this has been know to cause some models to balloon right up.  If it is, then either turn it off at the render settings, or turn it off for each body part of your model or prop.  The latter is more time consuming if you have many objects in your scene.

And you are right, displacement must be handled very carefully and set to a proper value to offset the bloat problem.  I have seen it on a skin texture displacement map while setting that value too high (0.5 inches).