The majority of major suspension builders have a good insurance policy to cover them for wrongful death suits.

Also all of them I know of are sold as "offroad use only", so if the customer chooses to run the product on the street they accept the responsibility for what "could" happen. One of thier products fails and you kill yourself or someone else all the manufacture has to say is "it was susposed to be used offroad only".

I know for instance all of our own line of suspension componets clearly state with the directions a clause to protect us; as it's required by our insurance company for them to even insure our business.

As for building your own I really don't know what to tell you. If you bought a kit you could probally get yourself out of a lawsuit by stating it was a purchased kit from someone else and with the proper proof I bet you could get away with not being responsibile. With a kit you built that would be a bit harder to do. I'm however not a lawyer or an insurance company so I'd say check with them prior.

I would have to say though, I think it would be hard to prove that if a product failed and you hit/killed someone that someone could prove it broke prior to the accident and wasn't simply damaged due to the accident.