Why wouldn’t you?
You must have some ulterior motive. I doubt you’re doing it out of the goodness of your heart, because you sound so officious, like you’re trying to reel people in by offering this free advice, only to later sell them some service and/or product that they didn’t bargain for.
I may be wrong of course about your intentions, but when people ask me why I shouldn’t trust them, this question in and of itself makes me wary of them and their game.
I’m not trying to discredit you or cast any aspersions on you. But I know and stand by this old, time honored adage: there’s no such thing as a free lunch.
I also fully get behind Bev’s suggestion, which obviates the need for your free service:
‘Buy from official sources and don’t trust strangers’