I've had few problems on e-bay; I've gone by faith, questions, intuition....
I can see your concern. Italian bikes, any high priced bikes, moreso frames can be faked, I've seen the stickers too and I've read plenty here and other places.

I'm knowlegeable enough and tricky. Still though, just recently, I've been more wary than ever. CL may be the way. It depends on availabilty, your area. I've not many prospects for used bikes near me.

Casatis are less apt to be faked, mainly because they don't command the price and due to the fact that there're many out there. Past few years an importer or two has let 'em fly. It's an exception for sure. Pricier brands can make lesser models, stickers stating higher level tubesets can be used to raise the price hundreds.

Look in local listings for a place selling used, a store that specializes in that. Again, it depends.
I'm looking at a Bianchi now; no intention of buying it, never did. The seller admits that it's bent. It's heading towards $300. Hit it now, it's ending soon. Road Bikes catagory, srranged in ending soonest. That's my thought for now. Catch you later.