I'm offered a replacement for my Galaxy S7(non-edge) version for a display issue. Is there anyway to know whether the replacement is refurbished or not without opening the box?
It will depend on the age of the phone they're replacing. With most carriers, if it's over two weeks old you get a refurb, because they're replacing a used phone.
AFIK, you can't tell from the box. All my TMoUS replacements have come in generic white cartons. I've had experience with both TMo and AT&T openly disclosing if it is a refurb, though. It would depend on what carrier you have, too, I would assume.