The bootlegged Godzillas tend to have crazy/contrasting paint jobs, and do not come with tags. With that in mind, it is fairly easy to attach tags, real or not, to vinyls with a special hang tag gun. So fakes may look like the real deal.
A bootlegged Spiega (tarantula from Son of Godzilla, DAM, and Final Wars) just sold on eBay for around $80. It even had an attached tag and was being passed off as a Bandai theater release. Bandai never released a standard size Spiega figure.
If you're ever after a certain sculpt and question whether it's legit or not, drop a line here or check the archives at
http://www.clubtokyo.org. Lots of knowledgable collectors around who can help avoid buying the fake stuff.
The Gamera theater exclusives can't seem to stabilize in price. The Bandai TE '95 and '99 versions jump from $35 -$100 all the time. Having patience and keeping a lookout will pay off with Bandais tho, since they consistently fluctuate.