Mitzvah of Bar Metzra on Buyer or seller

Does the mitzvah of Bar Metzra require a seller to turn to his Bar Metzra neighbor prior to putting the house on the market, or is the mitzvah upon the buyer to speak with the Bar Metzra neighbor prior to purchasing the house and to sell the home to the Bar Metzra neighbor in the event that he already purchased it?

The mitzvah of Bar Metzra is upon the buyer and not the seller. Nonetheless, we advise the seller to consult with the Bar Metzra neighbor in order so he can find a buyer, as who will want to buy a property that has a lien by a Bar Metzra who can usurp the property from him.

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See Smeh C.M. 175:7 “The law of Bar Metzra was not established upon the seller but rather on the buyer, that he should abstain from buying the property and hence, this consequently forces the seller to sell to the abutter.”; Smeh 175:38 “the institution of Hatov Vehayashar was not intrinsically instituted on behalf of the seller, as he can say that he does not want to sell the property at all”; Smeh 175:63 “although we already explained that the law of Bar Metzra was not instituted upon the seller, nonetheless, he should offer the property to the Bar Metzra for his own benefit, as his chances of success in selling the property is diminished until he asks the Bar Metzra, as people on the outside will fear buying is perhaps the Bar Metzra will afterwards usurp the property from them.”; Rashi Bava Metzia 108b; Pischeiy Choshen 11:49