Ebay is an advertising medium, not a shop.
Buyers need to do their own research - it is simply impractical to police this place because it would take an infinite number of experts to cover all the products.
You know a bit about stamps, I might know LED light bulbs, somebody else knows a certain brand of teddy bears. But there are millions and millions of items listed every day, and probably several hundred new ones appear every hour, where nobody is an "expert" yet.
And also remember - the photo in the listing need not be the photo of the actual item being sold. So you cannot just rely on what you see.
If you are an expert in a particular field, one of the most valuable things you can do is help create Ebay Guides. Take a look:
http://search.reviews.ebay.com.au/?satitle=stamps&ucat=260&uqt=g