Correct, there is no "industry standard grading guide" but IMO rainbows arer bred for color and the brighter ones are in greater demand, therefore the higher prices on those specific animals.
Quite often I will give a pair discount and for me that's more of a your buying in quantity so youe get a price break.
Snakes cen be inbred from the same litter. I see salmons advertised as F5's which is 5 gens of breeding from one pair of original animals...
P1 being two unrelated animals
F1 is first gen offspring
F2 is siblings bred together offspring
F3 is offspring from two F2's etc.
Once you breed two unrelated animals together you start all over again.
I label my babies so people (myself included) can see where they came from so they can make that decision for themselves. Too much inbreeding csan lead to genetic defects as well as the traits being bred for.
One other point Jeff already mentioned, from a breeder standpoint a female is more valuable than a male.
Exception being morph males, early on in the project, they can and will have a higher price tag since they can breed multiple females. One hypo male and three het hypo females is less expensive than 1 het male and three hypo females for example. That tends to drive the value of the male up. Once the market is saturated with males, it switches the other way around and now females are worth more.
Really follows the laws of supply and demand!!
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Thanks,
Dave Colling

www.rainbows-r-us-reptiles.com
0.1 Wife (WC and still very fiesty)
0.2 kids (CBB, a big part of our selective breeding program)
LOL, to many snakes to list, last count:
26.49 BRB
20.21 BCI
And those are only the breeders 
lots.lots.lots feeder mice and rats 

