A ranking gives you one number, but that number is built from parts. Each part measures something, and each part carries a weight that decides how much it moves the total. Two sources can both say a company scores well and still disagree about what matters, because they measured different things or weighted them differently. Before you shortlist anyone, find out what went into the score.
Write down your own priorities first
Start with your situation, not the ranking. Note what you most need from a softener purchase. Maybe it is a fast response when something breaks, clear pricing, a long parts commitment, or a unit sized for a large household. List your top three or four concerns in order. You will use that list to judge whether the ranking reflects what you care about.
Check which criteria are measured
Look for the list of criteria. A good ranking names each one and explains how it is measured. If a criterion is only described as quality or value with no explanation, you cannot check it. Note which of your priorities appear on the list and which do not. A ranking that never measures the thing you care about will not help you with it, no matter how high the total is.
Check the weights
Next, find how much each criterion counts. A ranking where one factor carries most of the total can hide weak results on your priorities. If service response matters most to you, a company that scores well on everything except service response may still be a poor fit. Compare the weights against the order you wrote down. Where they disagree, adjust your reading of the total.
Compare on criteria, not on the total
When you have two or three candidates, put their results for each criterion side by side. Look for the gaps. A company with a modest total but strong results on your top priority may suit you better than the leader. Also check that the scale is applied the same way to every company. Scores that cannot be compared across the whole list do not tell you much.
Check how the ranking was built
Ask whether the page says where its information came from and how it was gathered. Ratings that state their method let you test their claims. Ratings that do not are harder to rely on. The St. Louis company ratings on this site are built from published criteria, and you can read those criteria and their weights in the rating methodology. Start from the St. Louis company ratings page, then check each company's result against your own priority list.
What to do with the result
Once you know what the score measures and how it weighs those measures, use it as a filter, not a verdict. Shortlist the companies that meet your priorities, then get written quotes and ask each one the questions your priorities raise. A rating narrows the field. It does not replace your own comparison.