Keil & Delitzsch

It is now, for the first time, that the petition compressed into the one word שׁפטני (Psa 26:1) is divided out. He prays (as in Psa 28:3), that God may not connect him in one common lot with those whose fellowship of sentiment and conduct he has always shunned. אנשׁי דּמים, as in Psa 5:7, cf. ἄνθρωποι αἱμάτων, Sir. 31:25. Elsewhere זמּה signifies purpose, and more particularly in a bad sense; but in this passage it means infamy, and not unnatural unchastity, to which בּידיהם is inappropriate, but scum of whatever is vicious in general: they are full of cunning and roguery, and their right hand, which ought to uphold the right - David has the lords of his people in his eye - is filled (מלאה, not מלאה) with accursed (Deu 27:25) bribery to the condemnation of the innocent. He, on the contrary, now, as he always has done, walks in his uprightness, so that now he can with all the more joyful conscience intreat God to interpose judicially in his behalf.