Well when i got my GT28 for my leggy i gots it from APT.
There was NOTHING on it that "said" Garrett.
There was only one little metal tag that says Garrett and other junk on the center section.
Well there is one way to see if its a Garrett... Install it and drive it HARD!! If it dont spool great and not sound like the world is going to end its not a Garrett.
Here is a kinda crappy pic of my turbo in my car.
You can see in the box there that its totally blank. Yours has some writing on it. Thats a better indication that is real. Aswell yours is not been buffed to shiny finish.
Aswell the turbo looks to have nice beefy flanges. I had to mod some hardware to make mine fit because of how fat they were. Thats another good sign.