How do I avoid losing to lower rated players? I'm a Class B chess player. I'm afraid of playing low rated players because if I lose my rating goes drastically down. Sometimes low rated chess players are underrated or they play really good one game against a stronger player.
First, losing is part of chess. If losing didn't suck, then winning wouldn't rock.

Ratings are approximations. Don't let your rating define you.

The way to prevent lower rated players from defeating you is to not allow them to do so. Improve your play such that you can adequately punish the superficial hope-chess moves that "C" players play.

edit - There's no magic wand wand we can wave to help you. There is only working harder so you can play better moves.