Answer:
the principle of "express or implied contract" could be applied.
Explanation:
According to this principle, a contract can be legally binding even though no written statement was made by the offeror (in this case represented by Peter).
Based on this principle, Peter's act of publishing an advertisement on Ikman.lk can be regarded as an expression of sale. However, by virtue of ownership, Peter can thus decide not to sell his Wagon since no direct offer was made to John personally.