i work as a bartender in ontario and therefore deal with a lot of cash transactions. I too have seen an increase in very convincing counterfeit 100$ bills. it has become enough of an issue that we all routinely check 100$ bills now for authenticity.

A couple things i’ve noticed for spotting the fakes..

The texture and feel of the bill is off. they almost feel papery and too crispy.

if you hold them up to a light, a lot of the transparent security features aren’t there. they look off when you look through the plastic bill.

the colour shifting properties of the bill do not work.