i recently bought some uber cheap cards at a market (i know stupid but hey i decided to trust the 80+ year old Scottish man who was selling them)
anyhoo stupidly i didn't look at the packaging for 1 and failed to realise it said '2098 world championships decks' on the back there was spelling mistakes spelling 'every' as 'euery'
my first sign of them being fake was my machoke card which was named machole, fearing the inevitable i turned towards the serebii.net cardex
after looking the cards up on the card dex i realised just how stupid i ended up being as the information was WAAAYYY off, all the cards from 2 of the 3 items i bought had hp ranging from 100-800 and retreat values 6 times greater then what was featured on the cardex.
the booster pack i bought was the closest to legit bunch of fakes i found with 9 out of 10 cards matching the images and information in the cardex except for 1 which had a completely different attack then the site scan.
quality goes some of the fakes are really well made using good card stock(fakes being a slight thinner grade of paper compared to a legitimate card which is closer to a business card thickness) and printing techniques to emulate the originals save for a few which had noticeable blurring on text and images and slightly lighter/darker colours from a duplicate in another pack they were pretty impressively made.
so the moral of this story is if the packaging has windows (cut out sections to see the top cards) check the hp if its in the high 100-800 range the pack is fake, also check for spelling errors
i hope my experence will help you all in avoiding paying for counterfiet cards.
Thanks
EDIT: I Mentioned urls being fake i have discovered that i was wrong turns out what i thought was a fake url was infact a legitimate one used for earlier sets 'go-pokemon' the newer boosters use the official site pokemon.com so i apologise if i have mislead anyone