How do we know whether an individual has truly repented for their sin?

Jeff Pollard explains in this video that distinguishing false repentance from true repentance can be a challenge. Is there one, sure-fire element that makes it clear that repentance is true?

While there may not necessarily be one, sure indicator of repentance, there most often is a subsequent change in the life of a person following repentance. There is an abandonment, a forsaking of sin and a corresponding pressing on in love for Christ to honor Him. That person now has a desire of honoring God and a love for His ways. 

Matthew 3:8 (NKJV) – “[B]ear fruits worthy of repentance.” 

Distinguishing false repentance and true repentance can be quite a challenge. Sometimes they look very much the same. Is there a one surefire element that makes it clear that something is false or true? And I would say ultimately it comes down to this. There's a change in the life.

There is an abandon in the forsaking of the sin and pressing on in love for Christ to honor Christ with a heart desire of honoring him with a life knowing that we have dishonored him. But there are numerous other ways of trying to distinguish it. Sometimes it's a lengthy process in an individual as they struggle before the Lord.