What makes a bad user story?
Stories Violate Any INVEST Quality Criteria
Haven't been discussed, questioned, or negotiated (or you skipped the conversation) Have no value to the customer or end users. Don't have enough information to be sized or estimated by the team. Too big.
How do you know if a user story is good?
The story always elaborates an advantage for the user, customer or client. The story is quantifiable: it has enough concrete detail to enable an experienced team to appreciate its scope. The story is the right size. The story contains enough information to allow it to be tested.