I need to start by saying that I am NOT an attorney nor have I ever played one on TV. These are MY OPINIONS learned from the Law School of Hard Knocks.
Know your customers!!! If you get a bad feeling from them there is more than likely a reason. Meet with new customers at their place of business. It is amazing what you can learn standing next to a receptionist for 5 minutes while waiting for your contact to appear.
I have never had to test this advice but the what I have been told is that the more you know about how the parts you make are to be used the more responsible YOU are if they fail. Make your customer responsible for the design by NOT getting involved beyond what you need to know.
I require my customers to provide CAD files of ONLY the part they need made. The files must list materials, methods (weldments etc...), heat treat and surface treatments that I am responsible for, all listed in a separate layer on the drawing. If it is not in that ONE layer it is provided by other OR not required. I am not and will not be their "Engineer". And since I do not do welding or heat treating anything that comes in that indicates that a part is to be welded OR heat treated I "No Quote". My customers usually remove the offending information and submit a new RFQ.
The point is that what I have in my files is a drawing for a "widget". What that "widget" does or how it may be used is not my concern. It's rather like selling bolts to a company that resells them to an auto company. How am I to know if the bolts are to be used to hold on a license plate bracket or a brake caliper? If I can not begin to guess how that bolt is to be used how can I be libel for it's failure when misused?
Again... I AM NOT AN ATTORNEY!!! You should seek competent legal advice on this matter if you have ANY doubts.