Yep, I tune crap for my friends and fam, even snowboards. You have the right idea taking them in, they won't sand them but ask them to do a base grind and structure. The base of a ski is the same principal as a golf ball with the divots, you need a micro-structure so the snow can travel from front to back. If the base is slick with no micro-grooves, it will suction to the snow, kind of like how it feels on a spring slush day. The base structure needs to be done at the shop unless you have some mad tools and are a total tuning gangsta!
But do have someone teach you, it's very rewarding to tune your own gear. Sharpening edges is important too as well as checking your bindings. You trust your life with the stuff, you should be intimate with it. And, if you do it yourself, you have the luxury of keeping different temp wax on hand so you can check conditions the night before and wax accordingly. The first day out this year I still had yellow (warm) wax on from my last spring day and they sucked, fortunately my Karmas had purple (cold) wax and I just went back to the truck and switched rides.
Learn the craft bro, it adds to the passion. Glad you're interested.