1. The grey is from the very short hair (stubble) left on your face. It sticks out after a shave if you don't shave close enough.

2. As mentioned above, too much pressure and the wrong angle are the culprit.

3. The items you are buying are new, so there is no need to disinfect or clean them.

Trying a variety of blades from a sample pack has been mentioned, and that is a good idea. The Shark blades are not good enough for everyone.