Hope this is helpful
Blinking can often indicate nervousness, apprehension, fear even. A cunning boxer in the ring waits for the eyes to close before delivering a connecting blow.
Some Presenters, interviewers, news readers, doctors, surgeons, politicians, religious people charity fund raisers etc etc, deliberately use blinking to make their words more believable and are trained to do this along with raising eyebrows and other body language to emphasise a point. However, IMO it makes them less credible and to me usually indicates they are concealing some truth.
Body Language: How to Spot a Liar!http://eliothoppe.com/articles/20071029-body_language.html
Now it is important to note that the average person has a blink rate of approximately 20 blinks per minute. This number will vary slightly between people. That is why it is important to note that when you first meet with anyone, you must immediately begin calibrating their body language through simple observation.
When someone is relaxed, so will be their blink rate, at whatever their "normal rate" is. Make a mental note of their normal blink rate. Look at the pupils as well. If they are interested and engaged, the pupils will be dilated, even in a well lit area.
In fact there is a whole science about how we use subliminal suggestion to relax others. For example, if we are blinking a lot we let the person we are communicating with feel less threatened and more relaxed.