How can an employer find during interview session that the candidate is speaking truth or just for getting job he is molding himself?

During an interview, it is important to establish a connunication link with the interviewee, this helps to acertain their use of body language so as to establish effective communication. When an interviewee is telling the truth the tend to be confident at look at you in the face and they do not fidgit, but when the truth is lacking they look away, blush their eyes more frequent than before and sometimes end up stammering

Regarding to one's experience & qualifications, it can be verified by original certificates.  Job knowledge & skills can be examined thru written and oral tests.

With years of experience, employers knew very well that generally30-40% of the stuff in the CV are fake and the candidates main aim to get a job. The question asked by interviewers are generally checking on the personality, behaviour, subject knowledge and confidence level to accomplish certain projects. The educational and experienced certificates are all subject to authenfication from the issuing authorities.

Through eye contact and confidence level of the prospective employee tells whether he is telling truth or lying. 

Of the features of the face of his way to speak

Modern interviewer review past experience & emphasis that interviewee speaks himself, successful interviewer always allow interviewee share experiences, n that supports him to guage reality and guess either interviewee is trustworthy or not.

Before interview:

- Thoroughly review the Resume.

- Note down / highlight key activities which are relevant to our requirements.

During Interview:

- 'Interrogate as layman' about his background, job expertise & relevant knowledge.

- Observe interviewee 'body language', 'eye to eye contact', and 'facial impression'.

- Ask him very relevant & technical 'THREE QUESTIONS'.

- Just to Puzzle him, Get references from his last job (show him you will ask them you contribution).

if a person is shattered or overreacting that's mean (i think) he is not reliable otherwise trustworthy person ready to face anything. 

At the end, it is up to interviewer how he judge the people.