Gittin 58 - Buying a field in earnest
Three boxes of head tefillin, measuring together about 1,000 liters, were recovered from the victims of Bethar.
If one acquires a plot of land from an oppressor and then acquires it from the owner (by paying him required ¼ of the amount), it is not valid. He has to acquire it from the owner, and then from the oppressor. The owner's sale needs to be recorded in a document with title insurance. Then we assume that the owner was sincere.
Similarly, a buyer of a field designated for ketubah should acquire consent from the wife and the field from the husband.