There are always risks to buying on eBay, especially if you are new to the game. I only buy glass paperweights and know the field, so I've never had a problem as I generally only buy French, Murano, Scottish, American, or English weights.
It's difficult to actually advise you without naming a number of eBay sellers who are calling items Murano that are definitely not Murano. And, I don't think we are allowed to do that here. Usually these phony Murano items start at bids of .99 cents or $1.00, with shipping at $25 and $35 to avoid eBay fees. Some have photographs of Venice in their item description, but the items are made elsewhere.
True classic Murano, or great contemporary Murano pieces are highly valued and are not inexpensive.
I don't know if Frank will allow this name to stay, but there is one zany but decent U.S. seller who has written essays about fake Muranos in her contributions to eBay's Reviews Sections. She sells under the name Chinchchin, and you can find her by doing a seller search. She is an avid glass collector (has thousands of items in her personal collection) and sells a lot of things from various makers and eras. She's a colorful character, (her florid item descriptions are legendary), but her reviews and guides to real and fake Murano make for interesting reading. You can find these by finding the Meet The Seller section at the top right hand of any of her Item description pages and clicking on Review and Guidelines.