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I'd use length of time in business in a minor way. What if you found a spa that was "the one" for you, and it was offered by a dealer just starting out. The guy down the street has been in business for 12 years, but you found those spas to be only "okay". You gonna compromise on your spa just because the guy selling it is a newbie? I'd say it would be a factor, but not even close to a primary one. I'd say that the brand is more important that. A Sundance, Hot Springs, Jacuzzi, etc.. no matter what happens to the dealer, it's likely you'll get service even if your dealer closes up shop. The dealer I got my Optima from left the spa business this fall, but a new dealer opened up right across the street from them. Regardless, there is an authorized service center in the area who can do Sundance warranty work.
Local Caldera dealer been in business for 2 years. Owner has been servicing Watkins spas for 14 years and services the spas himself.Local Marquis dealer has been in business for 4 years. They also service their own spas although I bellieve their service guys has only been doing it for a couple years.In contrast, the local Hot Springs and Jacuzzi Dealers are both established have been in business 15 to 20 years. Neither service the spas themselves, both contract the servicing of spas out to third parties.