This is the advice I give out about trimmed cards. Buy some cheap commons and trim them using a few different methods, like guillotine paper cutter, scissors, exacto knife, ect.. You can even use one card and trim each side with a different method. Now label these card(s) how you trimmed them and now you have a reference to go to. Also get at least a 40X loupe to examine the edges. I know others will say lesser power will work but in reality it don't work as well. I also use one of those cheap 60-100X top lighted microscopes. Put the card in question in the middle of a stack of good cards and slide the top lighted microscope across the side of them and see if the side of the card in question looks the same as the known good cards. This last thing also works great at detecting reglossed cards as they always get a little gloss on the sides and it sticks out like a sore thumb under 100X. Hope this helps.
EDIT: Almost forgot about fake cards. A cheap fake can be determined by taking a wet paper towel and gently rubbing in on the card front. Water will not hurt most real cards but will smear the holy heck out of a home printer fake. If it is a rescreened fake with real ink made on a printing press it is a little harder but not much once you know what to look for. Most of us have huge TVs now. Take at least a 1200DBI scan of the card and a known real card and hook your laptop up to your TV. Now compare the print patterns on that huge TV screen. At that size even super good counterfeits stick out like a sore thumb.