buy a fish from your LFS. once it dies, take it back before the guarentee is over. they'll test your water for you to see if they'll refund it for you. if your conditions are good and they refund your money, you'll know they are trustworthy and test your water for real, and not just making things up to sell you stuff.
the number one mistake for new hobbyists are that they listen to their LFS. i had a friend who got into the hobby, set up a tank, and added a brain coral all in one day under normal flourecent lights, just because the LFS told him too.
so be careful out there.