Leadfingers. The problem was that in those days divorce could only be obtained by act of Parliament. V expensive. As a wife was considered part of her husband's goods and chattles, the belief was widespread that he had the legal right to sell her as his property.

A couple of interesting references.

Wives for Sale. Samual Pyeatt Menfee. Blackwell 1981.
E.P. Thompson. The Sale of Wives. In Customs in Common. Merlin 1991.
Also, if I recall correctly, there's a couple of books called News From The English Countryside, which contain newspaper reports of the sale of wives.