John Gill Commentary Psalms 129:8

"Neither do they that go by say, The blessing of Jehovah be upon you; We bless you in the name of Jehovah." — Psalms 129:8 (ASV)

Neither do they which go by say, the blessing of the Lord [be]
upon you
As was usual with passengers, when they went by where mowers, and reapers, and binders, were at work in the field in harvest time; who used to wish the presence and blessing of God with them, and upon their labours; and who returned the salutation, as may be seen in Boaz and his reapers, (Ruth 2:4) ;

we bless you in the name of the Lord ;
which is either a continuation of the blessing of the passengers, or the answer of the reapers to them;

so the Targum, ``nor do they answer them, "we bless you",''' &c.

The sense is, that those wicked men would have no blessing on them, from God nor men; that no God speed would be wished them; but that they were like the earth, that is covered with briers and thorns; which is nigh unto cursing, and its end to be burned.