I also agree with Johnstoni and have found that the vast majority of posters - myself included - do usually take care to make it clear in their postings whether or not something is opinion, an overheard snippet of gossip, or fact. The forum is an incredibly interesting, enjoyable and informative place (for the most part) and very often, the combined contributions of several posters end up answering a particular question which, on their own, no single member would be able address.
Obviously, like all other internet forums, you are never going to be able to guarantee 100% accuracy here ..... short of having a hotline to each and every zoo, as well as a raft of experts. However, I personally don't see anything wrong with rumours being repeated here - so long as it's not done maliciously. Interesting debate (and reading) can arise out of rumours even if they do later prove to be unfounded.
Bear in mind as well, that this is a forum which attracts both professional and amateur users - some of which are still very young. Interested amateurs by definition aren't experts, but their enthusiasm and eagerness to learn is what makes (for me anyway) this site such a joy to visit because inevitably someone better informed than them will invariably step in and correct them (tactfully and constructively for the most part). It's therefore inevitable that people will post up incorrect info because they have relatively little experience or knowledge of a particular topic but it's not intended to mislead.
I do understand it might be frustrating for some to see others commenting or criticising something they haven't seen but again, most people who do this seem willing to be set straight if necessary and are entitled to their opinion based on the information available to them. This site is a fantastic resource allowing many of us a glimpse at other zoos all over the world which we will probably never be lucky enough to see for real. I've found that other members familiar with such zoos are usually only too happy to share their experiences of them and extend others' knowledge. It would indeed be very dull if we had to restrict our thoughts and comments to places we have literally set foot in.
Of course, if you see something posted up which is incorrect - please say so ! Unless other members get feedback about their mistakes, they will continue to believe them.