Job 15:31 New English Translation

³¹Let him not trust in what is worthless,^[a]
deceiving himself;
for worthlessness will be his reward.^[b]

Job 15:31 tn The word, although difficult in its form, is “vanity,” i.e., that which is worthless. E. Dhorme (Job, 224) thinks that the form שָׁוְא (shavʾ) conceals the word שִׁיאוֹ (shiʾo, “his stature”). But Dhorme reworks most of the verse. He changes נִתְעָה (nitʿah, “deceived”) to נֵדַע (nedaʿ, “we know”) to arrive at “we know that it is vanity.” The last two words of the verse are then moved to the next. The LXX has “let him not think that he shall endure, for his end shall be vanity.”
Job 15:31 tn This word is found in Job 20:18 with the sense of “trading.” It can mean the exchange of goods or the profit from them. Some commentators change תְמוּרָתוֹ (t^emurato, “his reward”) because they wish to put it with the next verse as the LXX seems to have done (although the LXX does not represent this). Suggestions include תִּמֹרָתוֹ (timorato, “his palm tree”) and זְמֹרָתוֹ (z^emorato, “his vine shoot”). A number of writers simply delete all of v. 31. H. H. Rowley (Job [NCBC], 115) suggests the best reading (assuming one were going to make changes) would be, “Let him not trust in his stature, deceiving himself, for it is vanity,” putting “his palm tree” with the next verse.

New English Translation (NET)