There are two major ways to distinguish them:
(1) Observing the foiled back of the rhinestones
Swarovski, Czech, and Asian crystal rhinestones all comes with a silvery frosted foiled back. Picture shown as below:
While a plastic, or resin rhinestones, comes with a glossy silver back, as below:
It is really important to know how to distinguish the two kind of rhinestones before you buy it. Resin rhinestones are much cheaper in price, but it can be easily scratched and lost its luminosity because of the relatively softer material (Resin) used when producing the stones.
Crystal rhinestones are more expensive, but it's more durable and has a longer lasting luminosity.
Make sure you know which rhinestones you're buying before you pays for it, some Sellers sell resin rhinestones as expensive as crystal ones to make big profits.