The Japanese Takahashi cat figure appears in many different forms, some of which are obvious knockoffs of popular Kliban forms.  The walking cat bank is probably the most common rip-off, and frequently sold as a Kliban when it's the newer Takahashi.  The Kliban bank cat trails his tail behind him, and the face is different.  The tuxedo coffee/tea pot is another common rip-off copy.

As a long-time collector of the Kliban figures, I've seen many auctions with ceramic cats of mistaken identity.  Of course the surest protection is not to buy these hoax cats. 

Familiarize yourself with the genuine article, looking at the pictures of genuine Sigma pieces and memorizing what the real cat looks like.  It will make the fakes very obvious.  The head will often be the wrong size in proportion to the rest of the figure's structure - the Kliban coffee pot actually has a rather small cat head compared to the rest of the pot, but the Takahashi will be proportioned differently.  Ceramics with the original Sigma label are usually assured to be original, although a crooked seller could recreate the label and put it on a sham cat.

I hate to see these cheaters prosper, and worse yet, I hate to see collectors cheated.  Read the feedback, deal with well-established sellers, and if the cat looks funny, check it out to the max.