In reading through these posts, I've seen some naive comments about one's liability as an engineer.
Stamping (sealing) is not the only action that creates liability on the part of the engineer. If you are licensed, you are held to the licensing standard (the statute) in your practice, without regard to the actual act of stamping. Read your statute carefully....I've read quite a few of the statutes around the country and many are similar. In almost all instances, an "engineering service or work" is statutorily defined and requires a seal whether you think you can negotiate it out contractually or not. A contractual agreement does not override the statutory requirement.
As an example, let's suppose you do the calculations and design necessary to place or replace windows in a structure. You tell the client that it will be X dollars for the service or it will be X+Y if you must seal any part of your work. Client says he only wants to pay X so that's what you charge and you give him the design. You did the same work that you otherwise would have sealed but for the client's unwillingness to pay. Now comes a construction defect claim that the windows leak. You don't worry too much because a leaking window does not necessarily mean it is structurally deficient; however, in the process of evaluating the claim, another engineer reviews your work in the course of the investigation and cannot find anything sealed by an engineer. Knowing that windows are usually considered part of the components and cladding and can be critical to the structural design efficacy (whether the building is considered enclosed or partially enclosed), someone decides to chase you after they have figured out that you provided an engineering service, whether sealed or not. Now you have two problems....first is the fact that you probably violated your state law by not sealing your engineering work, and second, you are part of a construction defect claim that might or might not have validity to your work, but nonetheless you have to prove and defend it.
Be careful. Know your state's laws and rules. Don't let clients subvert your statutory requirements. Liability tentacles are often long and probing.