It depends on what kind of claims they’re making. I do, inherently, put more faith in a brand I’ve heard about than one I’ve never heard of, but I think that is true with anything (unknown vs. known) — but it doesn’t convince me to try it.
I hate when one brand will rant about another brand or put it down. I’d rather hear about what makes your product great than why another brand sucks. I dislike it when associates gossip in front of customers or talk about customers as they leave. It also encourages me to leave quickly if there is no acknowledgement.