I guess the only real way I know of is to purchase from a reputable breeder. Or you get a dog whose family tree can be traced.

 

Hello & welcome. Enjoy your stay!

 

Hi & Welcome to the forum. You can also post a picture in this forum and get some help.

http://www.germanshepherds.com/forum/pb-mix-rescue-posts-review/

 

Hello and wecome to the forum. Post pictures here, or here: General Information - German Shepherd Dog Forums

and people will give you their best-guess. No real way of knowing for sure without papers.

The link that Mac's Mom posted below is reserved for pictures of dogs that are in need of rescue. Individual owners looking for feedback on their dog, whether pure-bred or not, can post pictures anywhere. Post them in only one place to avoid confusion. Good luck!