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Every lot that enters my operation gets the same inspection, because fakes have gotten genuinely good, good enough that "it looks right" no longer counts as checking. I've caught counterfeits a few times over the years, almost always buried in bulk lots where a seller counts on nobody checking card #214. This is the routine.
The light test
Real Pokemon cards are a sandwich: two paper layers around an opaque core. Hold a suspect card in front of a bright phone flashlight, a real card glows dimly and evenly with the light mostly blocked; many fakes blaze through bright because they're single-layer stock. Edge-on under light you can often see the dark core line on a genuine card. This one test catches the majority of cheap fakes in seconds.
Font, saturation, and the energy symbols
Put the suspect next to a known-real card from the same era. Counterfeit tells I've personally seen: slightly wrong font weight in HP and attack text, oversaturated or washed-out colors, and energy symbols subtly the wrong size. The back is often more revealing than the front, the blue swirl pattern on fakes tends to be too dark, too light, or blurry at the edges.
Texture on modern hits, and what a scanner reveals
Modern full arts, alt arts, and rainbows have an embossed texture you can feel and see under angled light. Fakes either lack it entirely or imitate it with a generic dot pattern that ignores the artwork. A side benefit of scanning cards for listings: at high resolution on screen, wrong texture and soft printing jump out even harder than in hand.
Weight and size
A standard card weighs about 1.7–1.9 grams, my digital scale is part of the routine for anything valuable. Fakes drift lighter or heavier. Size: stack the card with known-real ones; a card standing proud or short of the stack, even fractionally, is a red flag. Neither test alone convicts, but combined with the others the picture gets clear fast.
If you've already bought fakes
Marketplace protections are your friend: eBay's money-back guarantee and proxy dispute systems generally side with the buyer on counterfeits, document with photos immediately and report the listing. And never resell a known fake "as is": knowingly selling counterfeits is illegal, full stop. The best defense stays upstream, buying habits and seller vetting, covered in how I evaluate lots.