Is there a way to tell if I am getting N-class Endlers in my LFS?

It would likely be very difficult to find N Class Endlers at most LFS. There are a couple of reasons for this, the biggest reason is it’s difficult for them to provide the documentation showing that they are the progeny of the Endlers that came from Venezuela.
The true definition of N Class is as follows:
“Any Endlers Livebearers (and progeny) that can be shown to have originated from their native waters in Venezuela will be considered to be a “Class N” Endler.”
It is very difficult for a LFS to provide such documentation. This is one of the reasons that we have our Breeder/Keeper Registry. The registry helps keep the documentation and chain of custody unbroken.
Another reason that LFS have a difficult time keeping N Class Endlers is that they often keep them in tanks with other livebearers such as guppies. Keeping other livebearers or even other Endler strains in the same tank can contaminate the strain.
While there are many breeders that offer N Class Endlers for sale online, there are few that can actually show the path back to the native waters from which they came. We have also seen several occasions where Endlers are listed as N class when they are clearly hybrids.
For example you should never see something like “N Class Tiger Endlers” as Tiger Endlers (at least as they are known today) are a product of Endler/Guppy hybridization.