When you do work as a consultant, prepare contracts for the work you perform for clients, and see to it that they are signed before you begin the work. If your branch of engineering has a standard "boiler plate" type contract, start with that and modify it for each project you take on. Make it extremely clear what is included in your services, and what is not. Make it extremely clear what you will be responsible for, and what you will not. Make it extremely clear how you will be paid and when, as well as what additional services may be outside the scope of your work. Include a clause, if you so desire, how disputes will be settled (mediation, arbitration, etc.), to try to keep the lawyers out of it as much as possible.
As Jimbo said, anyone can sue you for anything they want to, but it makes it pretty difficult for them if your position on goods & services is spelled out up front.