Condition
The condition of the toys are ranked like other collectibles: mint, near mint, excellent, good, etc. A Beanie Baby's value goes up the closer it looks to having come right out of the box. Stains, discoloration and damaged ribbons or tags will all reduce its value.
Authenticity
Beanie Babies will be worth more if proof of authenticity is provided, since there are counterfeits. An authenticated toy is packaged in a clear plastic box with a certificate of authenticity.
Retired Versions
Any Beanie Babies that are retired will be far more valuable. This includes the original nine of Brownie Bear, Pinchers Lobster, Legs Frog, Squealer Pig, Flash Dolphin, Splash Whale, Chocolate Moose, Patti Platypus and Spot Dog. Ty provides a list of its retired toys.
Tag
The red, heart-shaped logo tag is considered the most important factor in a Beanie Baby's value. A missing or damaged (even bent) tag will greatly reduce its value. Cutting off the tag is said to cut its value in half.
Rarities
A few toys were made slightly different than the rest of their type. Some were made without tails or details like spots, and some were given different names (like Brownie the Bear being called Cubby). These rarities are usually considered more valuable.