How to know it's real?
First thing to look at is the price. If it's cheap, it's most probably fake.
Perfectly trapped insects are also a sign of fake amber. If caught by boling hot resin, insects would try to escape.
Also, insects are generally to be found in only 1% of the amber on the global market.
If it's too transparent, too homogenous and simply too perfect, it's probably fake or compressed amber (made of amber residues and waste).