"It appears that tategoi, koi destined to be great, are comparatively light in colour when small with a strong, solid body and uniformity from the head to the tip of the tail. A relatively high percentage of koi with too bright a red retire early. I think the patterning is likely to disintegrate"
"When we cull, pattern is surprisingly a secondary factor: emphasis is placed on bone structure, even in small koi. There are koi that appear big for 20cm and koi that appear small even when they actually do measure 20cm. I believe that koi that appear big make good tategoi and that pattern is completely secondary"
"I select koi with good bone structure even if the pattern is simple since koi like these tend to possess elements that give them a comparatively high added value. It seems to me that a "tategoi" with a good pattern and too bright a red stands little chance of doing well."
-Hiroji Sakai, SFF
Hi guys,
The above are quotes extracted from an interview with Mr. Hiroji Sakai (Nichirin 95-1, No.329, May 1995). Hope it offers some help from the master himself on selecting tosai.

Every serious hobbyist has to tread his/her own path and pay their dues before developing an eye for quality koi, especially tosai. You can take the word of a dealer, even reputable ones, only to a certain extent before deciding for yourself.
Cheers,
Dennis