They are creative thinkers, and would often rather do things their way than yours. Boxers need attention and occupation or they can become destructive. Basic training in obedience and household rules is NOT optional for the Boxer. At a minimum, he must reliably respond to commands to come, to lie down, to stay, and to walk on or off leash regardless of temptations. Boxers can be a little too rambunctious for families with small children.
Boxers can also suffer from bloat and gastric torsion.
All dogs, of whatever breed, require significant upkeep costs, and all can require expensive veterinary emergencies. As an alternative to buying a puppy, you may want to consider adopting an older rescued Boxer. Most rescue groups have skilled evaluators who screen dogs for temperament and provide remedial training, veterinary care and neutering before offering them for placement, and who offer continued advisory support afterwards. Contact your local Boxer Club to learn who is doing Boxer rescue work in your area. The life span of a Boxer is about 10 - 12 years.