Firstly, let's deal with Romans 3:7
"3 What if some were unfaithful? Will their unfaithfulness nullify God’s faithfulness? 4 Not at all! Let God be true, and every human being a liar. As it is written:
“So that you may be proved right when you speak
and prevail when you judge.”[a]
5 But if our unrighteousness brings out God’s righteousness more clearly, what shall we say? That God is unjust in bringing his wrath on us? (I am using a human argument.) 6 Certainly not! If that were so, how could God judge the world? 7 Someone might argue, “If my falsehood enhances God’s truthfulness and so increases his glory, why am I still condemned as a sinner?” 8 Why not say—as some slanderously claim that we say—“Let us do evil that good may result”? Their condemnation is just!"
Notice what I have underlined:
1. Paul is not admitting to deception, he is speaking of a person arguing in the manner that is described.
2. Paul is addressing the claims of his opponents who are FALSELY accusing him of deception and are suggesting the aberrant teachings as viable.
3. Paul condemns their behaviour as worthy of receiving judgement.
The context is a far cry from Paul admitting he is a deceiver, he is actually addressing those are claiming he is a deceiver.
Now for 2 Corinthians 2:14-21:
"14 Now I am ready to visit you for the third time, and I will not be a burden to you, because what I want is not your possessions but you. After all, children should not have to save up for their parents, but parents for their children. 15 So I will very gladly spend for you everything I have and expend myself as well. If I love you more, will you love me less? 16 Be that as it may, I have not been a burden to you. Yet, crafty fellow that I am, I caught you by trickery! 17 Did I exploit you through any of the men I sent to you? 18 I urged Titus to go to you and I sent our brother with him. Titus did not exploit you, did he? Did we not walk in the same footsteps by the same Spirit?
19 Have you been thinking all along that we have been defending ourselves to you? We have been speaking in the sight of God as those in Christ; and everything we do, dear friends, is for your strengthening. 20 For I am afraid that when I come I may not find you as I want you to be, and you may not find me as you want me to be. I fear that there may be discord, jealousy, fits of rage, selfish ambition, slander, gossip, arrogance and disorder. 21 I am afraid that when I come again my God will humble me before you, and I will be grieved over many who have sinned earlier and have not repented of the impurity, sexual sin and debauchery in which they have indulged."
Paul is not actually admitting to trickery, he is actually responding to the accusation of trickery in the context. He even sent Titus previously and certainly Titus was not guilty of exploiting the congregation or tricking them.
It has also been noted that by others, Including Sam Shamoun of Answering Islam, that Paul is using sarcasm in verse 16. Shamoun states the following in his response to Bassam Zawadi:
"Paul was not admitting to his opponents’ claims, but was reprimanding the Corinthians for believing these slanderous lies about him when they should have known better and been the ones defending him. This is why virtually all commentators agree that Paul was using sarcasm and irony in 2 Corinthians 12:16 in order to embarrass the Corinthians for believing the slanders raised against him:
I did not myself burden you (egw ou katebarhsa umaß). First aorist active of late verb katabarew, to press a burden down on one. Only here in N.T. Crafty (panourgoß). Old word from pan, all, andergo, to do anything (good or bad). Good sense is skilful, bad sense cunning. Only here in N.T. and Paul is quoting the word from his enemies. With guile (dolwi). Instrumental case of doloß, bait to catch fish with. The enemies of Paul said that he was raising this big collection for himself. Moffatt has done well to put these charges in quotation marks to make it plain to readers that Paul is ironical. (Robertson's Word Pictures of the New Testament; online source; underline emphasis ours)so say the false apostles of me; for these are not the words of the apostle in his own person; nor to be understood of any spiritual craft, or lawful cunning and prudent artifices used by him, to allure and draw the Corinthians into a good liking and opinion of the Gospel and of his ministry, and so caught them, and was the happy means of their conversion; but they are spoken in the person of the false apostles, charging him with a wicked and criminal craftiness, by making use of other persons in a sly underhanded way, to get this church's money, when he pretended to preach the Gospel freely; to which he answers in the next verse. (John Gill’s Exposition of the Bible; online source; underline emphasis ours)" (Sam Shamoun, To decieve or not to decieve: http://answering-islam.org/Responses/Osama/zawadi_paul_deceiver.htm).
But be it so, I did not burden you…
These words are not spoken by the apostle in his own person of himself, but in the person of his adversaries, and contain a concession and an objection of theirs, but be it so; they granted that he had not burdened the Corinthians, that he had took nothing of them himself for preaching the Gospel; they owned that he had preached it freely; this was so clear a point, and so flagrant a case, that they could not deny it; yet they insinuated to the Corinthians, and objected to the apostle, that though he did not receive anything from them with his own hands, yet he craftily and cunningly made use of others to drain their purses, and receive it for him; and which is suggested in the next clause:
nevertheless, being crafty, I caught you with guile;
Hope this answers the objections.