Am I selling my soul to the Devil by practicing?

The only instances I find of people supposedly selling their soul to the devil is to deal with the devil for black magic or to something unnatural. One example would be to keep from getting old. Fictional stories about selling your soul to the devil make for an eerie and fascinating story, but I cannot find proof that it is true for people who wish to work with white magic. If you are looking to get into something darker or more sinister, then you are on your own ?
Here are links to a few fictional stories for your entertainment. However, these are all labeled as Black Magic stories.

http://www.sacred-texts.com/neu/hoe/hoe2-52.htm
http://www.sacred-texts.com/neu/hoe/hoe2-53.htm
http://www.sacred-texts.com/neu/hoe/hoe2-54.htm