I'll just explain it..... G1 or F1 means that the parents of the fish in question were wild-caught. The wild caught parents would be considered F0 or G0.
Offspring of the F1 or G1 fish are considered F2/G2...and on...
You can really see a difference between fish closer to wild generations and general tired old in-bred stock found in most pet stores and definatly in chain stores. You'll generally see brighter colors, more pronounced lines and patterns, even bars, full fins, robust body shape... in the fish closer to wild generation.
To get wild-caught fish or fish guarenteed to be F1/or G1, you gotta find a diver/breeder who can prove to you the origins of his breeding stock. The best way to find these breeders is to go to a Fish Convention and do a little networking.
I got all my fish directly from a diver/breeder who has pictures of him and Ad Konigs hanging out at Ad's conservatory... pictures of them diving, pictures of the fish they caught, pics of him packing them bringing them home.... etc. He even let me work with him for a few weeks to learn about the biz.