If they look clean and you can see the swirl in the glass I would lean more likely Venetian than Japanese.

As for dealers selling something as Japaneses or Czech they would most likely not get the same prices.
On ebay just because it says Venetian it seems to carry a premium. Dealers call everything Venetian because of this.
Whether its done intentionally or out of ignorance who knows.
As in all purchases its buyer beware.