The short answer to your questions is no and no.
To the untrained eye (i.e. mine and probably yours) one piece of glass looks pretty much like any other so, unless you are an expert, it is going to be very difficult to tell the difference between a well-made replacement that is not OEM compared to one that is.
If it were me, I'd ask them to show you a couple of phones where they have replaced the screen and if they looked as good as new and worked properly, I'd take a chance with them. Short of sending it back to Samsung, you will never know if any repairer will use OEM glass.