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please sit down; please have a seat
どうぞこちらの椅子におかけください。
Please have a seat in this chair.
受付が済みましたらこちらにおかけくださいませ。
After you finish the reception, please have a seat here.
お客様には空き席におかけくださいとお願いした。
She asked the customers to please be seated in the available seats.