Ask to see the relacement parts, if the seller can't show you the parts walk away.
Mass merchant spas can be a good buy, just do your research on who will repair them. Research the componants. Generic are generally the easiest to obtain and the most cost effective. Oem are the opposite.
Call the repair people and investigate what parts they have in stock, where would they come from, how long a wait would a repair be, what is and is not covered. Do your research.
Lots of dealers just want to sell you a spa and then wash their hands.