Shopping for a refurbished smartphone? Pay attention to its grade: It can make or break your purchase. Just like in school, refurbished phones get graded on a scale of A, B, C, and sometimes lower.

Just because you'll rarely find boxes of low-quality B-grade eggs sold fresh in the aisles of your local grocery store, it doesn't mean you're not eating them.

Go shopping for eggs at the supermarket (at least in the United States), and you'll probably notice USDA grades on the cartons. Yet often, you'll only see two grades: AA and A. If you happen to have ...