Personal attack: "Vendor X is a hack and an arsehole because I don't like his work. And I wouldn't be surprised if he smells funny, too."

NOT a personal attack: "Vendor X' work constantly shows fundamental flaws (Insert screenshots demonstrating those exact flaws here) so my logical conclusion is that he either is incapeable of delivering the type of quality I expect from a professional vendor or he just doesn't care." 

Actually, that's still a personal attack.  You're not commenting on the figure as much as you are on the vendor and his skills.
In this particular instance, the vendor claims the figure is "Poser the way it was meant to be".  Based on that claim, I expect to be "wowed" by the product.  I don't expect the product to be perfect but I don't expect to see basic fundamental flaws.  The vendors go on to point out their years of experience and how they are professional Poser content developers.  Shane has reminded us they are top rated content developers.  If they have that much experience, are professionals and are as highly rated as has been stated, then I do not expect to see basic fundamental flaws.  These are flaws I would expect to find in a new vendor who is attempting their first human figure.  In fact, if this were a new vendor attempting their first human figure, I would have given them more leeway because of their inexperience.