Earned-merits or trust points are not determinant factors for post quality of posters. They are only one of componental factors and they serve as supplementary inclusive factors for poster's quality assessment. Generally, to assess post quality of one user, readers have to consider lots of things:
Earned merit would be at the very top of the list when assessing someone's post quality. Earned merits means more than total merit as a lot of users got free merit for having over a certain amount of activity. In fact, I would think that a lot of users here disregard total amount of merit, and look at how much the user has earned in the last 120 days. Of course, is is combined with taking a look at their post history personally, but is normally the #1 indicator that someone is posting good quality content.
I agree merit is one of the greatest proof that a forum member is a good quality poster.
People wouldn't just simple give out merit unless they find your post helpfull and it is a quality post so having a high merit shows that you are indeed a good contributor to the forum (unless it is from cheating like buying merits).