I sold a few Won Park koi at last weekend's Cherry Blossom Festival. I didn't expect them to sell, but I sold out of what I had stocked (and had one stolen off the table, inside a coke container!). I felt they were expensive to buy (for a regular joe who thinks of paperfolding as "kid's craft" and nothing more), even though from a labor and artist perspective, I sold them on the cheap. Talking with Won after the Festival, I decided to follow his recommendations, which I have been reluctant to do for the sake of "purity"; and that is, to apply a bit of cement (from a gluestick) underneath the scales and the head. I am now sold on the results. I think there is more permanence on the model holding its shape over time and under humid and cold weather; which makes me feel better about people buying them from me. I dip the end of a twist tie (Won uses a toothpick, but I have none in the home) in the gluestick, then spackle it under the scales up top, and inside, underneath, as well as on the crimp in the head. It's well worth the efforts.
One of the biggest problems Won sees in how people are folding his koi, is in rounding out the model. Especially the head. The crimps help; but the fins should probably be folded back sharply, then the two edges bent and rounded together, as if one were going to close the bottom. Of course it won't close together (nor do you really want it to); but it will help round out the shape.
Really, I think the videos show this quite sufficiently well for all the complaints on them not being a tutorial.