Ask the seller to explain the purpose of all bands on the bird and to decode any numbers for you. There are many breeds of canaries and you could do a lot of research trying to decide which to get. It is best to buy directly from a breeder. To find canary breeders, contact a bird club, veterinarian, or look for ads in the paper. If you want a singing pet, then try to pick out a bird that you have actually heard singing.
Breeders are sometimes reluctant to let strangers into their bird room.
It helps to be a member of a local club, or be referred by a friend. To get a breeder to allow you into their home or aviary, assure them you are responsible and serious about getting a good bird. The more research you do and the more knowledgable you sound, the better your chances. Promise to call if you are late or need to cancel. Tell who is coming with you.