So What’s The Difference?
My dictionary defines earnest as..
a) a thing intended or regarded as a sign or promise of what is to come: In other words something of value given by the buyer to a seller as token to bind an agreement.
In fact earnest money deposits are involved in almost every real estate transaction. A check for a comparatively small amount of money is included when putting in an offer to buy a house. This check or “earnest money deposit” is designed to impress upon the seller that the buyer "earnestly" intends to purchase the property. It is good faith money, given to show serious intent to complete the transaction, If the prospective buyer changes his mind about the transaction he must be willing to forfeit the earnest money. However if the seller has, in some way, misrepresented the agreement or the item up for sale or fails to complete his end of the bargain, the earnest money can be returned to the buyer voiding the agreement.
Although the word deposit is not used in the original Greek, lets go ahead and define it anyway considering that the NIV uses it in all three verses.
The dictionary defines the word deposit as
a) a sum of money placed (in a bank?) usually to gain interest.
b) a sum payable as a first installment on the purchase of something or as a pledge for a contract, the balance being payable later:
c) a returnable sum payable on the hire or rental of something, to cover any possible loss or damage.
While both definitions do seem to have one meaning in common inasmuch as they can both be used to bind an agreement, using the word deposit tends to conveys the impression of a sum payable as a first installment on the purchase of something. This completely misses the significance of the word earnest which is not the first installment but given as a token to bind an agreement and regarded as a sign or promise of what is to come. Earnest money is good faith money.
In any case, neither a deposit nor earnest money provides a guarantee that the transaction will go through. Both can be forfeited or returned, depending on the circumstances. Yet the word guarantee has been inserted into all three verses.
While all three verses in question tell us that the Holy Spirit is the earnest, two of them mention being “sealed” by God.
in whom ye also, having heard the word of the truth, the gospel of your salvation,-- in whom, having also believed, ye were sealed with the Holy Spirit of promise, which is an earnest of our inheritance, unto the redemption of God's own possession, unto the praise of his glory [Ephesians 1:13-14. YLT]
who also sealed us, and gave the earnest of the Spirit in our hearts. [2 Corinthians 1:22]
And He who did work us to this self-same thing is God, who also did give to us the earnest of the Spirit; [2 Corinthians 5:5]
The word translated “sealed” is the Greek sphragizo, which is defined by Strong's Hebrew and Greek Lexicon as
Seals were used in ancient times to establish ownership and to verify that a document or other container had not been opened. It is used very similarly today as a mark of approval or authority (a legal document is validated by the seal of the State)..
We seal a letter by moistening the glue. A notary puts his seal on a document to attest to the fact that the party or parties involved actually gave the testimony indicated, or that the signatures are valid. When the tomb of Jesus was sealed (Mt. 27:66), it was for the purpose of fixing it so the body could not easily be removed. It was not meant to be broken, but note carefully that although it was not meant to be broken, it was. When we seal a letter, it is not meant to be opened before it gets to its destination, but it can be. When a notary puts his seal on an agreement, the agreement is not supposed to be broken, but it can be…
...When Abraham received "the sign of circumcision, as a seal of the righteousness of faith which he had" (Romans 4:11) God was attesting to the fact that Abraham and his descendants who kept the ritual properly, and obeyed the law would be His special people. It did NOT signify that they could not break His covenant, be disobedient and be cut off from the blessings promised. Surely no person who reads the history of Israel could logically conclude otherwise. 
Calvinistic theologians take the passages that mention the sealing of believers to mean that the believer is "sealed and secured" by God … a pledge that he can never be lost. In other words this sealing indicates the "eternal security of the believer". However Ephesians 1:13-14 says that this sealing by the Holy Spirit is an earnest of our inheritance”. Considering the definition of the word earnest, this interpretation is completely at odds with what the passage is saying... which is
The Holy Sprit is given to believers
1) As a mark to show that we are God’s people and are under His authority.
2) A valuable sign given as a token to impress upon the believer that God is in earnest about completing His end of the bargain. However this earnest can and will be forfeited if the agreement is broken.
The “Seal” in no way implies that we cannot break that agreement...
Consider the meaning of the word token which essentially serves as a symbol.. Either 1) a visible or tangible representation of something abstract or 2) a small part representing the whole. A token is never used as a guarantee of what is to come, but as evidence of the genuineness and capability of whoever gave the token.
Surely every Christian has to be aware (if they have thought about it at all) that the spiritual blessing he now has is a visible and tangible foretaste or down payment.. a small part of the whole future blessings God has in store for us. We have been given a token symbolizing that God is genuine about this agreement, is capable of carrying it through and is a small demonstration of the greater blessing to come
However there are no guarantees.. The Scriptures also warn that God gives the holy Ghost to all who obey Him [Acts 5:32] which implies that only those that obey Him are given the Holy Spirit.
We are also warned not to quench [1 Thessalonians 5:19] nor grieve [Ephesians 4:30] the Holy Spirit. When 1 Thessalonians 5:19 says not to quench the Spirit, it uses the Greek word sbennumi, used only a total of eight times in the New Testament... always in terms of extinguishing a flame
And the foolish said unto the wise, Give us of your oil; for our lamps are going out. [Matthew 25:8]
A bruised reed shall he not break, And smoking flax shall he not quench, Till he send forth judgment unto victory [Matthew 12:20]
where their worm dieth not, and the fire is not quenched. [Mark 9:44, 46,48]
withal taking up the shield of faith, wherewith ye shall be able to quench all the fiery darts of the evil one. [Ephesians 6:16]
quenched the power of fire, escaped the edge of the sword, from weakness were made strong, waxed mighty in war, turned to flight armies of aliens. [Hebrews 11:34]
Do not tell me that if the Holy Spirit is extinguished from a believer, He continues to abide within that believer.
When Does God Demand Return Of His Ernest
Whether the earnest evolves into a completion of the agreement depends, not on God who is perfectly capable of upholding His end of the bargain, but on us who often do not follow through with our part. As shown by countless Scriptures … only those that stand firm until the end will see the fulfillment or finalization of the agreement that was represented by the earnest. Scripture is with warnings about the consequences of falling from Grace by not persevering in the faith.
When we are disobedient to the teachings and commands of Jesus, we fail to keep our part of the bargain with God. Although at this time, He has every right to demand (take back) his earnest of the Holy Spirit, thankfully He is patient with us… “He is patient with you, not wanting anyone to perish, but everyone to come to repentance” (2 Peter 3:9).
When we sin and repent immediately God forgives and purifies… “If we confess our sins, he is faithful and just and will forgive us our sins and purify us from all unrighteousness” (1 John 1:9).
However we cannot presume upon His patience. We cannot sin with impunity and then confess our sins, believing we can then be forgiven and purified before God. The Apostle John warned, “No one who lives in him keeps on sinning. No one who continues to sin has either seen him or known him” (1 John 3:6).
See Eternal Life: Personal Possession or Promise?
 T. Pierce Brown. Sealed by the Spirit. http://www.oldpaths.com/Archive/Brown/T/Pierce/1923/sealed.html