First thing I would do is check the water at the LFS for yourself! If you want you can get them to check it right in front of you, but don't just take their word for the pH of their water! I have found each of my stores around here to be WRONG when they quote water chemistry to me. I'm not saying they are purposely lying, but one way or the other, THEY ARE WRONG. Bust them out by having them check it in front of you, if you can! That way at least they know the truth.
After you know their water chemistry.....
Less than .4 pH difference? I'd just take them home and add half a cup to the bag every 5 to 10 minutes until it is full. Dump half of it out and continue adding cups until full again. Then net them into your tank.
If it is a larger than .4 to .5 pH difference, I'd take some of (buy if necessary) the LFS water home and use that as your starting point. When you add them with the water to the aquarium, I'd let them sit for a day to ease stress first! The next day do a 10% water change using YOUR water and continue this each day for about 2 weeks. By then it should be pretty much fully your water. Start your normal methods from here!
This is all just what I would do if I were really worried about the fish.