"Be aware that there have recently been quite a few fake Shure SM58's on trademe, if you buy one of these you may as well just go down to Dick Smith and buy a $20 mic as that's all it's worth."If you have bought a SM58 on Trademe and are concerned that it's a fake then have a look at the pictures on this auction. In all these pictures the one on the left is genuine, the one on the right is fake. If yours is not identical to the one on the left in all aspects then 
you've got a fake.Take a look at the metal ring under the grille, if it is flat then it's fake. If it is contoured like the one on the left it could be real but it's still not gauranteed. And yes they even copy the warranty card too although this is different to the genuine one.
you've got a fake.Take a look at the metal ring under the grille, if it is flat then it's fake. If it is contoured like the one on the left it could be real but it's still not gauranteed. And yes they even copy the warranty card too although this is different to the genuine one."If your mic comes with a cable packaged in the box then it is also sure to be a fake as real ones don't come with a cable. Most of the fakes are of the switched version so if you have a bought a switched one then be even more careful.Lets face it if it seems too cheap then it's likely to be a fake, no-one in their right mind is going to be selling a real SM58 for less than $180 unless it's stolen or fake, just look at the cheapest price you can buy in the US, add on the shipping and do the maths!!"
Other references:
