Reliability

Question

Hi, Thanks for your interesting, if very brief, responses to to the important questions being asked by everyone here. If I see something posted on a web page (such as this one) saying that a certain food item is kosher or pareve or whatever, what is the law about "Ne'emanut", i.e. how can I know to trust an anonymous poster (or even someone who identifies themselves but I cannot verify)? I know 'Aid echad ne'eman beIsurim" but don't you have to know who the aid is? Or at least that he is Jewish and religious? Can saying you are religious on a web page count as Eidut which acceptable? thanks! Hanker