John Gill Commentary Ezra 4:13

"Be it known now unto the king, that, if this city be builded, and the walls finished, they will not pay tribute, custom, or toll, and in the end it will be hurtful unto the kings." — Ezra 4:13 (ASV)

Be it known now unto the king
And let it be seriously and thoroughly considered by him and his counsellors:

that if this city be builded, and its walls set up again, then will
they not pay toll, tribute, and custom ;
being able to defend themselves against the king's forces, sent to reduce them to their obedience; these three words take in all sorts of taxes and levies on persons, goods, and merchandise:

and so thou shall endamage the revenue of the kings ;
not only his own, but his successors';

this they thought would be a very striking and powerful argument with
him .