I wouldn't trust store salesmen as far as I could throw them. Most will just spew whatever they've been trained to spew. You may, on occasion, find someone who actually keeps up with technology and knows what they are talking about, but that's the exception. Sort of the same as finding someone qualified at Best Buy.
I think the best way to find info on a phone is to check out forums like these or go to the actual support forums for your cell phone provider or the phone manufacturer. There you'll see if there are any trends in terms of performance/issues/etc. Reading reviews and watching videos are nice, but those are easily manipulated or just short-term reviews that don't really put the device to the test.