The real transistor is the most modern version of the 2SJ162, made after Hitachi spun their semiconductor foundry off as it's own entity under the "Renesas" brand. Note the absence of Hitachi markings, or indeed Renesas. Note also that the real thing has it's marking done with a printing process, whereas the fake has markings done by laser, in a raster pattern.
Lots of transistors are marked by laser now - indeed it's the standard way for product to be identified these last fifteen years or so. However that's after Hitachi became Renesas. Note the real Renesas product (perhaps twelve years old) still hasn't got laser markings.
The other tell-tale is that the date code on the two wildly different 2SJ162 packages is identical. Fabs do change their packaging from time to time, but not with the same date code.
Note further that the raster pattern isn't just where the markings are, but extends all the way across the package. I'm hypothesising that this is how they obliterate the original markings without resorting to sanding.
And their counterfeit complementary pairs, 2SK1058s:
This is incredibly frustrating. I'm a seasoned professional engineer with decades of experience. If I didn't have some known-good stock of these transistors, and if I hadn't been alerted to the possibility of trouble by the two different 2SJ162s with the same date code, then I'd have chucked them in a circuit and wondered why it didn't work. How's a fifteen year old enthusiastic kid going to cope? She'll build her amp, wonder why it vanishes in a cloud of smoke, and give up.
A very easy test can be done with a multimeter. Cgs on the real parts is ~0.8nF, and Cgd around 0.6nF for the 1058, and 1.1nF for the 162. For the fakes I didn't measure valid capacitances for most of the 2SJ162s (so they probably aren't even MOSFETs), and the remainder all measured ~5nF Cgd, so they're likely DMOS parts rather than lateral MOSFETs.
So the last photo shows a cotton bud soaked in isopropyl alcohol, having scrubbed the surface of the transistor:
I'll see how the seller goes with a refund.
Edit: The seller refunded immediately, and said "Hello I sold many of this item, without any complaint", which is I guess exactly my concern. So lots of people have bought these, put them into amps, found they don't work, then blamed either their own assembly skills or else the amp design, when the problem is that the actual parts are fakes. It's really unconscionable behaviour.
Finally, a quick disassembly. From left to right we have both the flavours of "2SJ162" then the "2SK1058":