2. A liar will naturally add more detail to try and manufacture credibility. Do not interrupt. Let them ramble. Silence from you will solicit more imaginings from them.
I've heard the exact opposite, that a truthful account will include extraneous detail because those details are part of the true memory that the person is replaying in their mind.
That is not necessarily a contradiction. The reason that liars add detail is to mimick truth tellers, so it makes sense that truth tellers add details as well. The important difference is that truth tellers do not need to remember the details, because they already remember them, whereas the liar needs to remember the new details.
Having said that, as a lay person, I would be concerned about false positives. Memory is associative, so even with a truth teller, I would expect more detailed and accurate recollection when told in chronological order then reverse-chronological order.
I've heard the exact opposite, that a truthful account will include extraneous detail because those details are part of the true memory that the person is replaying in their mind.