A sales pitch describes the company you are meeting today. The model number a provider installs describes what you will buy for the next decade. Before you compare quotes, write down the make and model of every unit each provider proposes, then check three things about each one.
Check whether the replacement parts are sold by others
Ask the provider to name the cartridge, media, membrane or resin part numbers they will use for replacements. Then search for those exact numbers at two or more independent suppliers. If you find them in stock in more than one place, you are not tied to a single company. If the only source is the installer, ask what the part costs and how long shipping takes before you sign, because that cost and wait will repeat for as long as you own the system.
Check whether the manufacturer still lists the model
Look up the model on the manufacturer's site and note whether it is current, discontinued or listed with a replacement. A discontinued model is not a reason to walk away, but it is a reason to ask the provider, in writing, what they will supply when the parts run out and whether they will stock them or refer you elsewhere.
Ask whether they manufacture, distribute or resell
Ask directly whether the company makes the equipment, is an authorized dealer, or buys units from a distributor. Then ask who handles a warranty claim and whether the company can reach the manufacturer's support team without you acting as the go-between. The answer tells you how many steps a future problem will take and who controls each one.
Put it on the comparison sheet
For each provider, list the model, the replacement part numbers, the number of independent sources you found, the model's status, and who holds the warranty. Two quotes with similar totals can look very different once these rows are filled in. Our rating criteria are described on our review methodology page, which explains how we weigh these kinds of details.