Sorry I replied to the question that when being interviewed they ummed and ahhed a lot, that makes them guilty of not telling the truth. I replied with an article that stated that actually those using filler words a lot were proven to be telling the truth when they did an experiment. I don't know how success rates dropping has anything to do with it.
It's more that most scholars don't support Villar's research with regards to credibility and filler words.
It's not just "credibility" either there is research to contradict Villar's conclusions on "truthfullness". Such as:
Matsumoto, D., & Hwang, H. S., et. al. (2011) “Evaluating truthfulness and Deception: New tools to aid investigators”, FBI Law Enforcement Bulletin, (June): 1-9.
Navarro, J. (2008) “What Every Body is Saying”, New York, NY: HarperCollins Publishers.
Vrij, A. (2008) “Detecting Lies and Deceit: Pitfalls and Opportunities”, Wiley-Blackwell; 2nd Edition, ISBN-13: 978-0470516256