Two quotes can look close on price and still describe very different jobs. The quickest way to see the difference is to ask every provider the same questions, get the answers in writing where you can, and compare the answers rather than the brochures.
1. Who tests your water, and how?
Ask whether the provider tests your water on site or wants a sample sent out. Ask what the hardness reading was based on, and ask to see it on paper, including when it was taken and where in the house it came from. A reading with no test behind it is only a guess, and every sizing decision built on it inherits that guess.
2. How was the unit sized?
Ask which numbers went into the size: how many people live in the home, how much water the household typically uses, the hardness reading, and whether things like a second bathroom or a dishwasher were counted. Then ask what they would change if the household grew. A provider who cannot explain the sizing cannot defend it when the water runs hard during the busiest week of the year. The site's own method for judging providers is laid out on the methodology page, which is a fair checklist for what a sound comparison looks like.
3. What exactly is covered, and for how long?
Ask whether the warranty covers the tank, the control valve, the parts, and the labor, and whether each one has its own term. Ask whether the resin is covered and what the coverage period is. Request the warranty terms in writing before you sign anything. Two bids that both say 'warranty included' may cover very different things.
4. Who answers the phone after the install?
Ask for the name of the office or person you call with a problem, the hours they answer, and what happens if the installer no longer works for the company. Ask how they handle a call-back in their own words, and ask for the name of a nearby customer they have worked with. Also ask whether the installer holds any license your city or county requires for plumbing work, and ask to see it rather than take the answer on trust.
5. What happens if you leave?
Ask what you keep if you change providers: the manual, the model number, the install record, the warranty paper, and any service or salt arrangement. Ask whether any plan can be canceled, how much notice it takes, and whether a fee applies. The answer tells you whether you own the equipment in practice or only on paper.
How to compare the answers
Lay the answers side by side on one page and mark any question a provider skipped or answered vaguely. A short answer is not automatically a bad one, but a vague answer on the water test or the sizing is the one to press on, because those two decisions drive how well the softener works for years. Only after that should you look at price. If two bids differ in price, the cheaper one is only the better deal if its answers hold up on the same five questions. For a wider view of where this step fits in the whole purchase, the seven-chapter buyer's guide walks through the order most homeowners work in.