A softener is a long-lived purchase, and the brochure is the cheapest thing to read. Before you commit, check the parts an independent body has tested, because those marks are the one part of the listing you can verify yourself.
Find the certification on the exact model
Water softeners sold in the United States are commonly certified to NSF/ANSI 44 for softening performance. Ask the seller for the certificate number, then look it up in the certifier's public listing yourself rather than trusting a copy in the sales folder. Check that the listing matches the model number, not just the brand or the series, because a manufacturer can certify one model and sell a different one beside it.
A certification tells you the unit was tested to a standard. It does not tell you the unit is the right size for your water or your household. Keep those two questions separate.
Read the listing for the numbers it should state
Ask for the rated capacity, the regeneration settings the unit uses, the salt type it needs, and the water use per regeneration. If a seller cannot give those in writing, the sale is not ready. Ask whether the unit runs on a timer or on a meter, because that changes how it behaves when your water use changes.
Ask what the certificate does not cover
Ask whether the certification covers the control valve, the resin, and the brine tank, or only the performance claim. Ask whether any part sits outside the certification, such as the bypass valve or the drain fitting. Get the answer in writing with the model number attached.
Compare the same unit across quotes
Once you have the model number and the certificate, ask each provider to quote that exact unit. Two quotes for different models are not a comparison, even when the labels look alike. For how we check listings and what we count as evidence, read our methodology.