The easiest way to have a false assurance of salvation is to have a false doctrine of salvation. Because the person's doctrine is faulty, his or her assurance has no firm basis.
Also, a legalistic and self-righteous belief system will falsely assure people of salvation by believing they will get to heaven by trying to live a good life accompanied by good works.
So, back to the question, "Can a person be sure he/she possesses saving faith with full assurance? The answere is yes!
We must examine our own hearts to see if we have true faith in Christ. Do we have a genuine love for the Lord Jesus Christ? Such love for Him would be impossible without regeneration.
Also, we must examine the fruit of our faith. We do not need perfect fruit to have assurance, but there must be some evidence of the fruit of obedience for our profession of faith to be credible. If no fruit is present, then no faith is present. Where saving faith is found, fruit of that faith is also found. In conclusion, we seek our assurance from the Word of God through which the Holy Spirit bears witness to our spirit that we are His children.
Let me finish this post by referring to Rom 12:1 "...present your bodies a living sacrifice." OT sacrifices are no longer of any effect. For those in Christ, the only acceptable worship is to offer themselves completely to the Lord. Under God's control, the believer's yet-unredeemed body can and must be yielded to Him as an instrument of righteousness.
Lastly, (almost done) Paul does mention the doctrine of "conforming to godliness" (1 Tim 6:3) and that godliness is profitable for all things, in time and eternity (1 Tim 4:8).
Far from a self-righteous attitude (there is a difference) Paul also mentions over in 2 Peter 3:11, "...what manner of persons ought you to be." This is a exclamation rather than a question. It means, "How astounding excellent you ought to be!" This is a straight forward challenge for Christians to conform their lives to God's standards in light of the reality of coming judgment and eternity. Holy conduct refers to the way a Christian should live---separate from sin. Godliness refers to the spirit of reverence which should permeate a Christian's attitude---that which rules the heart.