Every provider can point you to happy customers. That is the point of a reference list, and it is why a list alone tells you very little. What you need is a short set of questions that past customers answer the same way, so you can compare providers on what actually happened in their homes instead of on how well the sales conversation went.

Get more than one name, and mix the sources

Ask for at least three past customers, and ideally from jobs that look like yours: the same type of unit, a similar water problem, a house of similar age, or a service call rather than a new install. If the provider offers only one name or says their customers prefer not to be contacted, treat that as information. Where you can, also look for a customer they did not hand you, such as a neighbor who used them or a local group where people discuss their experience with a given company. One chosen reference is a sales tool. A few unprompted voices are closer to a real track record.

Ask the same questions of every reference

Keep a written list and read it word for word on each call so the answers are comparable. Useful questions include:

What did they install or service, and how long ago? A job from a few weeks back tells you about the crew and the paperwork. A job from several years back tells you whether the unit still works and whether the company came back when it did not.

Did the work start and finish when the provider said it would? If not, what changed, and did the provider tell them before it happened?

Did the final bill match the first written quote? If it did not, ask what the difference was and who decided it.

When something went wrong after the install, how long did it take to get someone out, and what did that visit fix? Ask whether the problem was solved on the first visit or whether they had to call back.

Did the technician show them how to use the unit, what routine care it needs, and where the shutoff and bypass controls are?

Would they hire this provider again, and what would they change about the experience if they could?

Listen for specifics, not adjectives

Friendly, professional, and on time are cheap words. A useful answer names a date range, a part, a problem, or a call that went badly and how it was handled. Pay attention to whether the reference volunteers a rough moment. A customer who says the install was fine but the follow-up took a week to schedule has told you the follow-up is the weak point, which may matter more to you than the install. If a reference gets vague or changes the subject when you ask about problems, note that too.

Compare the answers in a grid

After the calls, write one row per provider and one column per question. Then look for patterns. A single complaint from one customer can be bad luck. The same complaint about delayed follow-up, surprise charges, or the same recurring fault from two or three separate customers is a signal worth weighing heavily. Do the same for praise. Repeated, specific praise for how a problem was handled counts for more than general enthusiasm about the equipment.

Know the limits of this check

Three to five conversations is a small sample, and each reference was chosen to some degree, even when you pick them yourself. Use the calls to find the questions that separate providers, then check your findings against other sources. If a provider's reviews repeat the same complaint your references mentioned, give that complaint more weight. If the references describe a problem the provider has never mentioned, ask the provider about it directly and compare how they respond. How a company handles a hard question is part of the track record you are trying to measure.