2) Polite requests. “Would you shut the door?” vs “Would you shut the door.” Again, many experts claim that this is actually a command, not a question, and thus should be punctuated with a period. Others say that, grammatically, it’s a question, and should thus take a question mark. Very long, complicated requests like this do well with periods. With shorter requests, however, you’re less likely to jar your reader if you simply use a question mark. Now if you want to jar your reader, that’s a whole other story, and a great use of a period. See below.
Avoiding Common Punctuation Errors Pt 1: Commas Save Lives; the Vocative Comma
Avoiding Common Punctuation Errors Pt 2: Commas and Periods in Dialogue
Avoiding Common Punctuation Errors Pt 3: Commas with Participial Phrases