I know for a fact that many fake ST Dupont lighters are being sold on eBay disguised as the real thing.  There are a few sure ways of telling if the lighter being sold is the real thing or not.

I have been a collector of Dupont lighters for many years now.  I also manufacture and sell The Best Brass Adapters to refill your ST Dupont lighters.
1.     James Bond 007 Ligne 2 lighters have serial numbers that are not etched or inscribed into the lighter rather they seem to be stamped by a fine gold like color pen.  The serial number should read as follows: xxxx/5007.  The xxxx should be a number from 1 to 5007 since there were only 5007 ever made.  These lighters should not have any serial number that has any type of letters in the serial.
2.    The above scenario is the case for any limited edition ST Dupont lighter such as for the Opus X, Teatro, Maharajah, Africa, Medici, and so...
3.    The actual weight of the fake lighters is also different.  The fakes actually weigh more than the original.
4.    Where you refill the butane, the inside seems to be different also.  The nipple where it releases the valve sits higher than the actual/authentic Dupont.
5.    Look at the feedback of the sellers.  The feedback is almost always less than 40.  The sellers have only been registered with ebay for a short duration.
6.    Pay attention to the serial number if it is a Ligne 2 lighter.  If the serial numbers line up perfectly straight and they are perfectly alligned, then it is most definitely a fake since the serial number was stamped by a machine rather than by a human.  The authentic ST Dupont lighters are hand stamped not by a machine.

More to come