> "That's too complicated"
> "I don't want to bore you with the details".
Response: "Try me."
Dig for the details and if the candidate can't provide them, then either someone else did the work, they used a library and don't actually understand it, or they made it up altogether. This is assuming, of course, that they did the work relatively recently (<5 years).
If they deflect by mentioning either IP agreements or NDA's, then remain on topic but discuss something else under the same umbrella. For example, if the candidate deflects a question concerning k-means clustering, then ask about k-nearest-neighbors. If they continue to deflect, that's a red flag.
I'm a pessimist when it comes to hiring, but there are a lot of imposters claiming undue credit in this industry.
I recommend finding the best bullshitter at your company and having that person interview the candidates with you. A good bullshitter can always spot another bullshitter.