Most test kits that use test tubes and "reactive" chemicals will give you better reads. The strips can be compromised fairly easily.
I use Saltwater Master Kit, personally. I don't know if there is a great difference.
Fish stores are just like anything else, in my opinion. Each person working there may have knowledge, though not neccesarily the knowledge you need! Trust yourself and if you don't recognize a fish, pass until you can find info. You'll save money and heartache.