I keep eyes on the various markets and haven’t ever seen any Koetsu bodies that would give me concern. I’ve had 6 Koetsu in my hands - about half from used market, some purchased new from dealer, most the the used ones have gone through rebuild via Koetsu Japan (who would have rejected counterfeits). I’m pretty certain a counterfeit (not just gray market; an actual counterfeit attempt) would look or feel quite weird in some way. The Koetsu bodies are very finely crafted.
I share concern in general about 2juki’s sources and practices, but not on the topic of Koetsu counterfeits.
What I do see is a lot of retipped Koetsu for sale! Sometimes just the tip, sometimes the whole cantilever. Sometimes this is NOT disclosed in the ad. You need to learn what these stylus mountings (and boron and joint pipe) should look like up close, and how to spot obvious 3rd party retips. Modern Koetsu uses a very clean interface fit, with (usually) minimal glue. The "mound of glue" mountings are not Koetsu. Vintage Koetsu aren’t as clean looking as modern, but still not a mound of glue. The mound of glue is a perfectly valid mounting technique btw, but it’s never been used by Koetsu. I believe Lyra’s diamond mountings look a lot like Koetsu’s - probably from the same Japanese supplier.
