I'm not a dealer, but I have a lot of residential wiring projects under my belt, including my spa.
You need to check with the electrical authority in your area to see if permits and inspections are required on electrical modifications, and to see if homeowners or other non resident individuals are allowed to work on residential electric projects.
This all varies by locale. Some places don't care, others won't let anyone do electrical work unless they are licensed. Most are probably somewhere in between the two.
The process I followed required two inspections- one rough in- where the wiring was inspected prior to covering it up and energizing it. And a second inspection after all work, including hooking up the spa, is completed.
The only people allowed to work on residential wiring in my city is the actual homeowner, or a licensed electrician. I'd bet most spa delivery people are not licensed electricians.
Find out what the rules are in your area, and if you are concerned about your hookup, ask to have it inspected. Small price to pay for the peace of mind you'll get.
Not to mention what kind of insurance hassels you may have to deal with if there ever is a fire, and they can't find records on the work.