I personally wouldn't bother running it in for a free wax. Waxing is so easy to do by yourself, and the job will be better, so even "free" wouldn't interest me. Also, if it's not a specialty ski/snowboard shop, who knows what monkeys they might have working on it, stripping a binding screw thread or whatever.
Also, my one and only experience with a belt wax was with a board I rented for my kid on vacation. The rental tech set it up for him and gave it a belt wax in front of me. When we got to the top of the hill, his board absolutely would not go for the thick layer of wax left on the base. I had to pull my credit card out on the mountain and use it to scrape all that wax off. Royal pain, but it was OK after that.