Welcome to the forum.
Make sure the used spa at least works. If they can't show you it works (pumps work, heater works etc) you may want to look elsewhere.
A new spa, read, research, read some more. Especially posts in here. (As an idea crosses your mind do a search, above tab. There will be many replies on the subject usually) Then come up with a list of what you want in a tub: lounger, foot jets, certain areas of your body that need more therapy, how many people . If you don't really need therapy just hot water you can go that route.
Then when you get your list of 'wishes' start brochure looking (you can start having them sent to your house now..word of caution, if you contact Master Spa (or is it Thermo spa?) get ready for a phone call barrage) to eliminate which spas don't have what you want. Then you can begin the wet testing. Don't 'fall in love with a name' (if you look through the forum you'll get an idea of which companies to avoid (part of the research phase)). The wet test will be more helpful than any spoken word. Seal the deal and start soaking.
IMHO if a dealer wont' let you wet test go to the next one. If a dealer doesn't make you feel comfortable or you don't trust them, move on.
Hopefully others will leave comments but that is my 2˘.
