Heck, most of the people who post here are on serveral sites, no surpise that competitors do also, anyone saying they don't visit competitor sites is lying. You should take it as a compliment and not a threat. Unless of course they are asking questions that they know will make you look bad, then.. yea, thats trolling.

otherwise, it's good business sense.

Out the person if you think it isn't in good faith, otherwise, why bother telling us about it.