Look for liquor control board signs... They are required by law. If there are WALCB signs then it's a no go... Also, there should be a firearms restriction sign that the LCB has been having business' put up. If there are no signs up, it could just be a business policy to be over 21, and carry would be Ok. Look up RCW 9.41.270, that has the specific language about restrictions on carry.
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