The words as you know
are linked to the denial (that Paul never used flattery) to affirm its truth in the minds of the Thessalonians. Flattery is something which is easily observed, especially by the one who is being flattered. Although some people may be taken in by flattery, it is not usually difficult to notice that a speaker is trying to flatter his hearer. Thus, Paul could appeal to the Thessalonians’ own knowledge for confirmation that he did not use flattery in his dealings with them.
5 For we never came with words of flattery, as you know, nor with a pretext for greed God is witness.