You will be fingerprinted and a criminal history background check will be conducted prior to issuing your Washington firearms dealer license. If your business is located in the unincorporated area of the county, then you must apply at the Benton County Sheriff’s Office. You can apply for a Washington firearms dealer license with the Prosser Police Department if your business is located in the City of Prosser. How do I apply for a Washington Firearms Dealer License? 923(a) is required to have a Washington Firearms Dealer license. RCW 9.41.010(10) requires anyone engaged in the business of selling firearms at wholesale or retail or who has, or is required to have a federal firearms license under 18U.S.C. When do I need to obtain a Washington Firearms Dealer License? Crime Free Rental Housing & Inspection Program.