PHOENIX – As shoppers prepared to snag some Black Friday deals, Valley police departments were preparing to keep the Black Friday peace. Officers will be on site at some stores and shopping complexes, where they say they hope shoppers will use patience and common sense during their bargain-hunting. But not all threats come from other shoppers: With some stores opening on Thanksgiving and staying open through the night, a lot more customers will be heading back to their cars in dark parking lots, creating another safety hazard.