I address this in Chapter 3 (3-I: Parts Availability), but this is an especially important concept when it comes to used hot tubs, so I’ll expound a bit here.
Obviously, antique hot tubs can be hard to find parts for, but that can also be true of newer hot tubs. Some proprietary brands change things up every few years and stop making parts for their older models. Since they’re in the business of selling new hot tubs, they really don’t care about consumers who bought a hot tub from them five or more years ago. It’s called “planned obsolescence”, which encourages people to buy new instead of repairing the old.
The more unique parts and features in a particular model, the more dealer-reliant you become, with model-specific parts that are eventually discontinued. This means repairs may require more expensive parts and special knowledge to work on.
Some cheap fly-by-night brands may go out of business, but even some established high-end brands make changes to their product every 5-10 years, discontinuing parts for their older models. So theoretically, if you buy a 4-year old model from a proprietary brand, you may not be able to get parts for it in 3 years.
It’s best to go with spas that use standard, easy-to-get jets, spa packs and plumbing parts that are not unique to that particular hot tub brand name.