What are the consequences for a man who sold a cow to a man he did not know, and then the cow strayed from the buyer's home back to his own, so he sold it and consumed its price because he did not know the buyer?

This cow, after the questioner's disposal of it, falls under the ruling of lost property (Luqata). He is obligated to announce it in the markets for a period of one year. If its owner appears, he should hand over the value of the cow he sold. If the owner does not appear, he should donate its price with the intention of guaranteeing it for its owner.