Loosely defined tategoi only means that it will improve... so at 3" the term can be loosely applied to almost anything that isn't obviously butt ugly

While yours will likely improve for a while (it is cute, not ugly) how much and for how long is the question. To the Japanese, true tategoi are too good to sell this year

. The Koi for sale to all but a very select few ought to be called "tategone" IMHO, because most of the time they're just about as good as they'll ever get. (just my non-expert opinion

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There is an important caveat to my last statement. We have some dealers who are members of this board. Take a look at their recent buying trip pictures. TateWOOHOO!!! Respected dealers (respected by the Japanese Breeders) get a better look than a newbie. They've earned it.
You mentioned that while you are still learning about skin quality (aren't we all?) there was something about this one that just looked "different". Higher quality skin does have a different look to it, but you'll have to read some of JR's, MikeM's, DickB's, BobW's posts on the subject to learn about it here. I'm learning how to see it, but I can't begin to put it into words the way they can.
All pet stores are not created equal, and they don't all buy speckldygoi from the lowest bidder. Some have had to start getting better quality stock (still not high end, but not as junky either) because their customers have started to wise up and demand better quality. At least now you can begin to find discernable varieties in their sales tanks.
I mentioned earlier that the pictures just weren't big enough to say much beyond "cute". You can't see the skin or the hi plates well enough to discern anything about it.
The beni should be darker in the center of the scales if it is of decent quality. It should look better at the head than toward the tail, and finish slowly in a head to tail progression.
The sumi should be barely emerging, hopefully developing at the tail first and slowly working toward the head, and finish in the same fashion.
In a Tategoi Sanke these two things will finish to their greatest potential at about the same time, hold for a season or two, and then say a long, slow, goodbye.
If someone comes along and tells you I got something wrong, pay attention... They're probably right

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