Hi, I have just received two fake Links of London charms from the same seller. 

Tips to spot a fake:

The link that hangs on the charm is a big give away.  It should be oval shaped with the Links of London hallmark on the side (three oval links), and another hallmark at the end.  The hallmarks should be clear, and well inset.  This link should also be oval in shape, and not round.

If you have already received a charm, you can tell whether it is fake or not from the weight too.  Genunie Links of London charms are quite heavy as they are solid silver, the ones I have been sent are light and tinny sounding. 

Also, compare your charm to the picture from the seller.  In my case, I ordered the bikini and the mantaray charms.  The pictures from the seller show different markings on the charms, compared to the ones that I have received - there were three spots on my bikini charm that hadn't even been coloured in!

You are more than likely not going to know whether the charm is real of fake, until you receive it.  With this in mind, I would recommend you purchase Links of London charms with caution.

I hope this helps.