"You can indeed tell your customers to send us some pictures of the broken models and also let the order number, this way we can create a complaint out of this and request to have the broken models reprinted."
So if you feel your parts are weaker than normally please contact Shapeways...
[email protected]
This will also help them to analyze and tune their SLS machine re-calibration cycles.
If you hit the wall with your car and break parts, I woudn't blaim it on SLS prints

Personally I'm not going to make a complaint about my front arm I broke after hitting a car just after big full speed double jump.
-Niki-