All Ty beanies have the same, glossy, soft fur, even when they're old. All authentic Beanie's ribbons are shiny on both sides and are sewn fastened. Check a real one for width and colour, these are common mistakes with fakes. Shades are often wrong, but you'd need to compare with a real one to see. Easy ones to spot are the 'speckled' ones like Billionaire, Kicks and 1999 Signature, as the colour is usually solid on the fakes.
Fakes often have the wrong colour nose.
There are a myriad of mistakes to look out for on tags. Often Beanies are found with tags they weren't produced with, or with a tag combination that wasn't found on authentic Beanies. Tags are found with a different generation outside to inside, for instance 5th generation font on the outside, with 4th generation text and layout inside. Even if this is OK, there are other things to check. Ty uses the same font on a given generation of hang tag and the spacing, layout and symbol placement are the same, so compare with one you know to be authentic.