In general the acquarium made in chine featured an unpolished base. It was probably the most easy sign of a fake. But during the last 2-3 years I have seen (in the shops of some friends, not in my one) some imported items with better details, first of all the polished base.
All the old Cenedese block that I had in my hands feature the fish made in furnace and not lampworked. It means that they are much bigger and thicker.
In general the blocks of recent production have different colours due to commercial issues (people prefer acquamare, tourquoise, blue).
At the end the best check, as usual, is the feeling when you have the piece in your hands.