Here are some Recaro SPG vs Fake comparison pics.
Pic above, Look at the line where cloth comes down to the opening of two belt loops. Its much closer to the opens than the fake. I checked with my Spirit R seats and its same as the black SPG pictured.
Also look at the shoulder sides. The cloth seems to be bit wider on the fake.
This particular replica uses small plastic surround for the belt loops.. but I've seen others use the same size plastics.
Again, look at the shoulder area.
Again, the shoulder area. Real Recaro seems to follow the contour of the shell where as the fake doesn't
At this angle I can't tell..
Nor this angle.
Kai is also right about the real one having a plastic surround at the bottom of the seat. Also, fit and finish seems to be much better on real vs replicas. For instances, look for signs of covers taken off the seats. Real Recaros will not have any excess cloth materials sticking out of the plastic loops in the back of the seat. Usually when you see that, it shows either someone took the cover off the seat (to either put the embroil the Recaro logo on) or just bad craftsmanship.
But as stated before, 'Real' Recaros sold by Recaros to general public will have a serial number on each seats. Some recaros sold to car companies either have this serial number or it may not. For instance, Spirit R and RZ seats.... When I contacted Recaro, they told me that they can not sell any replacement cover or cushion backs as its Mazda has the rights to them. Recaro makes them for Mazda but Recaro can not sell them to general public. And when Mazda sell those parts, it has a specific Mazda part number to them.
And when Recaro sells it to a car company, usually they are different in looks and shape. Example, Spirit R seats look similar but CF/K shell shape is different from the Recaro seat above (SPG.. actually one above looks like pole position).