A local shop might as well make things worse if they do not care too much and give your skis the standard treatment (e.g. different angle than before). Once you have a good edge, it's kind of similar as keeping a knife sharpened. No need to really grind every time, a fine polishing after skiing for a day is more than sufficient and makes your edges last a long time. Been using tools from here for 10+ years, they also have informative instructions: https://www.tooltonic.com/