Just received my S19j Pro today
Worked directly with Grace and @gracezhou1993 is her legit Telegram.
@minerexpertsales is there sales channel. They have at least one other reviewed contact some other forum members have worked with.

I actually paid for a future date December batch S19 90Ths unit (paid very end of Sept), and delivery was apparently delayed by Bitmain.
Also, Bitmain apparently shipped wrong units to minerexperts, (S19j Pro - various speeds) and up-charged based on speed and Pro version vs non pro to be delivered.
So I ended up having to pay additional $1600 to get unit.
Is what it is I guess
In the end, I did get the unit and Grace is legit.