It is in the 17th century and if you hate your wife or if your wife hates you then you can't divorce her. However, if you are rich and have money you can but then the process is long and financially draining so why should you. But then how do you leave your wedded partner for another? it seems in 17th century selling your wife was a good way to get out of a marriage you regret and that also includes the kids.
Why sell her?
Selling your wife was a tradition practiced in 17th century England as a means to get out of a marriage you didn't like. The poor man couldn't afford a divorce and the rich man could've but it would cost a lot and so people supposedly found "a loophole" in the system.
(gee how did they come to that conclusion)
The number one reason was that either one or both partners were fed up of the marriage and would sell the spouses. In almost all the cases it would be the wife which would be sold as back in those days wives would be seen as property by men. Sometimes along with the women, even the children would be sold off as some sort of bargain offer along with the kids.
Another reason would also be that the man couldn't provide for the family and therefore selling off his wife and kids to someone else would mean that he receive money in exchange and the wife would be with someone who could look after her and her kids.
Was this practice outlawed?
I wouldn't exactly say it was outlawed, but it was severely disliked and could land a prosecution. However as time went on the views on this began to change and husbands who sold their wives started recieving public humiliation and were seen as some kind of scum.
(Karma is a bitch right)
But you can't put all the blame on men as there would be some instances if the wife found another lover, she could tell her husband to sell her off to another guy and the husband would gladly agree. But the main point was that given how England at that time was conservative, it was really the only way out of a divorce.