Bianca, C. Massimo/ Bonell, Michael Joachim, Commentary On The International Sales Law, Art. 18, Milan 1987
167 2.3"

Thus an offeree's mere silence in the face of an offer to sell goods is not ordinarily an acceptance because the offeror has no reason to infer from the offeree's silence that he assents to the offer. Of course, if in addition to his silence the offeree takes some affirmative act, as where a buyer exercises dominion over goods shipped to him, that act may amount to acceptance.

Referring Principles
Trans-Lex Principle: IV.2.2 - Silence by offeree
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