Customer reviews can tell you more than a sales call, but only when you read them as evidence instead of a score. A softener company can collect a strong average from satisfied buyers and still give a poor installation. The useful questions are which stage of the job each complaint came from and whether the complaint describes something you can check before you sign.
Gather reviews from more than one place
Read reviews where people leave them without being asked, such as map listings, local community groups, and consumer review sites. Treat a company's own testimonial page as marketing. Note how many reviews each company has in total, because a handful of reviews in either direction can skew a small sample.
Sort each complaint by stage
Put every negative review into a stage: first contact, quote, sales visit, installation, service call, billing, or warranty claim. A pile of installation complaints tells you about the crew and scheduling. A pile of quote complaints tells you about pricing discipline. A pile of warranty complaints tells you what happens after the check clears. Each pile points to a different question you can ask.
Look for specific details
Strong reviews name the problem, the type of unit, what the company did, and what happened next. Weak reviews use only adjectives. A review that says the crew left the floor wet and the drain line unconnected is useful. A review that says the company was terrible is not. Give more weight to reviews that describe a step you can verify, such as a written quote, a named visit, or a part that was swapped.
Watch the reply, not just the review
Check whether the company replied to negative reviews, and whether each reply addresses the problem or only apologizes. A reply that asks the customer to post an account number in public shows how the company handles complaints. A reply that offers a specific fix and names the next step is worth noting in your comparison.
Spot the patterns that look staged
Be careful with reviews that all arrive in one burst, repeat the same phrasing, or praise the same staff member without describing the work. Be equally careful with a block of harsh reviews that all complain about the same thing without any detail. Neither pattern proves anything alone, but both are reasons to weigh the reviews lightly and look for more detail elsewhere.
Turn the reviews into questions
Take the top complaints in each stage and write each one as a question you will ask the company before you sign. Ask how the crew handles drain connections, who the installer is, and what the written process is for a warranty claim. Good companies answer those questions in writing. Companies that dodge them have already shown you their answer.
For how this desk weighs review evidence against other factors, see How We Rate Water Softener Companies. To compare the companies this desk has reviewed, start with Best Water Softener Companies in St. Louis, then check each shortlisted company's reviews against the stage-by-stage sort above.