I do emphasized that in all cases you should attempt to acquire a captive bred specimen. There are several reasons for this – first, captive bred animals are almost always healthier than their wild collected counterparts, being generally far less likely to have been exposed to such maladies as internal and external parasites and other diseases. Also, captive bred animals usually adapt more readily to being kept as pets. Finally, the plentiful availability of captive bred snakes reduces the necessity to collect wild specimens for the pet trade, thus relieving the pressure on the natural population. Although corn snakes are not endangered in the wild, it is better to leave them in their natural environment.
Your next choice will be whether to purchase an adult or hatchling snake. Although there are arguments to be made on both sides, it is generally better to start off with a hatchling for several reasons. First, there will be a wider variety to choose from. You will also know its age and, if buying directly from a breeder, its genetic background, which will be important if you intend to breed the animal in the future. You will be virtually assured that it has been captive bred, since very few hatchlings are wild collected. Finally, you will have the satisfaction of watching your snake grow and mature into its adult coloration.
Whether you are buying a hatchling or an adult, there are several items you should check to attempt to determine the animal’s health. Check that it appears alert and responsive as you handle it, making sure that it flicks its tongue in and out to check out its environment. Also check its body weight and muscle tone – it should not appear emaciated or have its ribs protruding, and should not have visible scars or “kinks” in its spine. Ask if it has been feeding regularly. Check its vent, called the cloaca, to make sure that it appears dry and closes properly. Try to listen to its breathing – if it appears to be wheezing or if mucous is present around the mouth, this may be a sign of respiratory infection. The mouth should close tightly and not display any scars or lesions. Finally, check the animal for the presence of any external parasites such as mites or ticks.