That's too bad, but it does happen. Were you buying it for resale, or for your own enjoyment? You must have liked it enough to pay the price you did...? If you derive pleasure from it, I'd say that's what really matters.

If you want to get a good idea for values, try searching completed items on ebay. You can sort by highest price. Prices vary wildly for Murano glass on ebay, but I'd say overall you can get a good idea for the types of pieces that are most desirable to collectors.
Try not to get discouraged! I think just about everyone pays too much at one time or another.