The state of the marriage can reveal not only the individual's level of happiness, but the amount of effort and faith he or she is willing to put into it.
A peaceful marriage suggests happiness. In Austen's novel many marriages have to undergo familial approval in order to stay on the social ladder. Love was not the first thing anyone considered, which is why Anne was forced to turn Wentworth away in her youth. However, if a marriage is actually peaceful it demonstrates the individuals' ability to compromise, communicate, and learn to love each other.
On the other hand a turbulent marriage suggests that one or both individuals are unhappy or unsatisfied. This could be a common problem in an arranged marriage, especially where a young girl is concerned. When there was no such thing as divorce, all we saw was the unhappy people trapped in a marriage. Their levels of tenseness, resentment, and anger could be evident or we may just see unhappiness and loss of faith in love.
When marriageable people could be scarce in your social circle you could adapt to what is available and be happy, or spend your life pining. Marriage served a high social purpose in Austen's novels. It kept families of similar status together and maintained the wealth within the same circles. If the husband was good at using and maintaining money, chances are the wife lived very comfortably and would be happy. Because marriage had such a tie to finance, the state of the marriage also reveals how well that household manages money. Much like today, the better money was managed, the happier the marriage is likely to be.