It is best to buy Chinese teacup pugs from a reputable breeder who treats his dogs as pets, keeps the dogs in a clean environment and offers a health guarantee that allows you to have the dog checked by your own veterinarian before finalizing the deal. You may be able to also get a healthy teacup pug from a local animal shelter or rescue group. A veterinarian may have information about trustworthy breeders, shelters and rescue groups.
The pug's coat should be dense, smooth, glossy and free of fleas. The cute wrinkles on a pug's face as well as its tightly curled tail are potential sites for skin infection. Carefully check these areas and be prepared to do this throughout the pet's life. Its eyes should be bright, but any discharge from the eyes or nostrils signals health issues. Pugs usually have breathing problems that at times need surgical correction, so check its breathing, and listen for any rattling or rasping. It is very important to get complete feeding instructions from the breeder, since a teacup pug needs to be fed small meals quite frequently.
You can also get a fair idea about the behavior and size of the pug by observing both its parents.