I had a similar question a while back
and I got the black Ergo Sport for $85. It was through Amazon, but sold by Sparkles Gift and Party Shop (which sounds really sketchy).
I was nervous but when it came I really scrutinized it and used a few blog posts that had real/fake comparisons. As far as I can tell, we got a real one.
The final thing I did was google both the merchant and the word Ergo (you can look up official dealers by location, but not by shop name as far as I can tell). Well, a blog post from the actual Ergobaby blog came up, listing a promotion and in it is a long list of participating stores. Now, my assumption is that these stores are selling real Ergo products (otherwise, Ergo would not be promoting them, right?) So I felt really good seeing the shop mine came from as well as Mod Parent which was another Amazon vendor that a poster said wasn't authorized to sell.
So, I am apt to use this as an "ergo dealer list." Here is the post: