I suggest that you look at the following section on Boxerworld.
This area explains about genetic testing (which is not cheap). You are looking at roughly (depending upon your area) approx $1000 - $1200 per dog for the testing. Some of the tests, need to be run EVERY TIME prior to breeding.
Generally, dogs that come from *pet type* breedings, can not produce dogs that are correct for the standards. (general rule of thumb.....a dog can not produce what they are not themselves).
You will not find a responsible breeder that has *good lines* sell you a puppy without co-ownership of the pup, or with full breeding rights. Responsible breeders have worked hard to develop their line and they do not want unethical breeding to ruin what they have worked so hard to achieve. A reputable breeder would take you under their wing, and guide you in breeding, showing, etc, if you are serious, but don't expect them to sell you a pup with full breeding rights outright.
Do you really know the difference between a show quality dog and a pet companion dog? The difference can be very minimal when dealing with a responsible breeder. The difference is very great when dealing with backyard breeders or commerical dog breeders (puppy mills), or Pet Stores.
Here is a few more links for you to look at: