Which products should you submit the identifier_exists attribute with a value of no for?

• A) Items as part of a bundle
• B) Used electronics
• C) New books for pre-order
• D) Custom-made clothing

Correct answer is:

• D) Custom-made clothing

Explanation: In the rare situation where your product has neither a GTIN nor MPN (for example, made-to-order or handmade items), set ‘identifier exists’ to ‘FALSE’ to indicate that you have no identifier for the product.

Read more here: https://support.google.com/merchants/answer/160161