The counterfeit market is increasing every year, and they're getting better and better with every batch. There are already an insane amount of fake Supreme x Air Jordan 5 Retros floating around, so if you're looking to purchase a pair in the secondary market...BECAREFUL! Thanks to Riley Jones (Complex Contributor) and @Fake_Education we can see a few details below that set the real apart from the fake.
The "SUP" branding on the midsole is an easy way to see whether they are authentic. On the real pairs, the netting should have a cloudy, "dull" look opposed to the fakes which are more clear and focused.
Another detail to pay attention to is the plastic lace lock. The authentic pairs should have a clearer, more transparent lace lock. The fake pairs look more milky or cloudy. Also note that the "Supreme" branding on the lace lock are much bolder on the fake pairs opposed to the real pairs, which show up more dull. Also note the placement of the Jumpman logo on the real and fake pairs are slightly different.
You also might want to check the branding stitches behind the tongue. The labels inside the tongue should be stitched and cut cleanly with littler variance between the two. Take note of the fake pair's inconsistency in the cut and stitch, which doesn't appear on the real pair. Also the spacing between the two labels are further apart on the fake pairs in comparison to the authentic pairs.
the rubber outsoles are another great way to determine whether they are real or fake. The outsole is much clearer on the fake pairs, and the supreme box on the fakes is much too large and spelt in an entirely wrong font. The supreme box is also a slight bit too close to the jumpman's left leg.
The Jumpman stitching on the authentic pairs are much cleaner and consistent. Note the fake pair's jagged edges that appear more fuzzy and uneven in comparison.
The iconic Air Jordan V shark teeth should appear thick and subtle. Notice the fake pair is much skinny, defined, and unbalance accent of white speckles.
Lastly, the "94" branding is placed a little too close to the midsole on fake pairs. Although, the font and shape are very similar so be sure to refer to other points mentioned above to make the finally call.