First check your box. It should show no signs of being bashed around. It shouldn't be overly shiny. Check the side, you should see a label with barcodes on. This shows it's from a reputable retailer.
Now the case. It should feel like quality leather and will be well stitched, with a shiny logo on the left side. The popper will also have a logo on it. A real case will have a hardened front too.
Now for the contents. The glasses themselves usually have a label from the retailer where you got them. A booklet of 'Icons'. A package containing the cleaning cloth and manufacturers note.
A closer look at the contents of a genuine pair.
A fake pair will probably come in a plastic bag. This pair had an unpackaged cleaning cloth and a fairly well made replica of the manufacturers note shoved into the case.
Now to the label on the lens. It should be shiny gold foil and the black logo should be perfectly centred and sharp. It shouldn't be a normal adhesive sticker but the kind that uses static to stick.
The Ray Ban engraving should look bright, bold and clean, it's pretty easy to see if it's printed on (you can scratch it right off). Also notice the difference in the shape of the silver bits.
The biggest giveaway is the hinges. True Wayfarers have the oversized metal ones. Fakes will usually be small, be made of plastic or low quality metal and will break easily.
The badge on the temple should be attached with pins going into the arms, rather than glued. It will be small and shiny. Also note the angle of the arms, it will be smaller than usual glasses.
On transparent Wayfarers such as these tortoise-shell ones you should see the metal arms inside the plastic ones (for extra strength). This is a simple way to tell, and as you can see, these are fake.
On the inside of the left arm there will be some info about your glasses. This is easily copied, however real ones will have this text right up by the hinge, fakes usually have it much further down.
If you check everything in these steps you should easily identify fakes from real ones. I hope this guide has helped you out and will make you think twice before spending £30 on a crappy pair!
Note: Most people would have a hard time telling the difference, so picking up a reasonable replica is a good way to save a LOT of money and still look fresh. Peace yo.