There is no use tax on guns....only sales tax. Use tax is recurring like property tax. We pay use tax on my commercial vessels home ported in a state. that are federally documented. It is the only way the state can collect a recurring tax.As I understand it (and consistent with my gun buying experience), if the firearm is new to Washington, whether from a business or a private party seller, the FFL doing the transfer must collect the use tax. If the firearm has already been subject to a use tax (i.e., paid when the firearm first came into Washington (and assuming it's being sold by a Washington resident) there is no additional use tax due on a sale within Washington.
And 123 Pawn in WW charges $15 for the transfer.