Thais use smiles to convey a wide range of emotions for which many Westerners would consider strange. If I was to generalise, I would say they are not fake, but rather outward coping mechanism for awkward or unpleasant situations. Other Thais would know exactly the true meaning.
Then Thais also smile for exactly the same reasons we do (some of which might also be considered 'fake' e.g. sarcastic smile), but many of which are genuine smiles of joy, happiness, and pleasure.
As with any foreign culture, if you plan on spending any length of time among it, it is best to learn the nuances so that you can function more effectively within it.