What to do if being sued for selling counterfeit items?

I would need to know a lot more before I could answer your questions.  However, if you have not had substantial contacts with or activities in the other state (the Complaint will indicate what the basis is for personal jurisdiction over you). it should be possible to have the summons quashed for lack of personal jurisdiction. Are you sure that the summons is not seeking testimony from you relative to whom you got the counterfeit goods from?  There are so much unknown information that it would be best if you find an attorney in the state in which the case is pending to help you and not knowing the state, I do not know whether I can help you identify a suitable attorney.