I assume this is going to be done in an interview. One thing you could try is to see how the person handles constructive criticism. Try to get them engaged in

I assume this is going to be done in an interview. One thing you could try is to see how the person handles constructive criticism. Try to get them engaged in a discussion about what they did wrong and how they could do better in the future. Pick something you have actual knowledge of so you can better tell if they are BSing you. This can be difficult to do in an interview because you often don't know anything about the person. However, even if you have them pick an example of a screw-up from their past, you should be able to get a general sense of whether or not they try to be accountable for their actions. A bad sign would be if they pick an example where they didn't actually screw up or explain their failure as completely out of their control.