Question mark or period to end a rhetorical sentence
Solution 1:
That particular sentence could be a question or a statement. The use of a question mark or period is what would actually determine that.
Correct:
Maybe you could be a security guard there and enforce whatever the WalMart policy is at that location.
Also correct:
Maybe you could be a security guard there and enforce whatever the WalMart policy is at that location?
Solution 2:
You would use a period at the end:
Maybe you could be a security guard there and enforce whatever the WalMart policy is at that location.
If we rewrote it as a question, then we could use a question mark:
Could you be a security guard there and enforce whatever the WalMart policy is at that location?