Not sure what you mean by “authentic” vs non, but I’ll take a stab and say that authentic magazines are quality controlled much more stringently as they are approved for reading by the general public.
Anything else and you’re really having to take some random person’s word that they (or their publisher) haven’t cut corners with something ranging from ineffective to downright deadly.
Anyone can haggle. The worst that could happen is the news stand operator will say no, or perhaps they’ll say yes but you’ll still get scammed.