1) You would be liable if you are at-fault in some way in causing the accident. That is, a part you manufactured or provided was defectively designed or manufactured, and that caused the accident; or your instructions for use or installation (if you provide same) were defective and caused or contributed to the accident; or you did the installation and that was defective; etc. You are not liable just because your parts were on a motorcycle in an accident: there must be fault on your part and a causal link between that fault and the accident.2) Insurance would be very helpful. To oversimplify, insurance would defend you in court and/or pay any amounts you are liable for (up to the policy limits) so long as you were not engaged in knowing or intentional wrongdoing (like deliberately selling parts you know to be defective, to save money).