The auxiliary verb hath is repeated here in Mosiah 10:18. In his editing for the 1837 edition, Joseph Smith removed the second hath. (He also grammatically emended the first hath to has, but this change is irrelevant to the discussion here.) The repetition of the finite verb is helpful since there is a long intervening prepositional phrase between the subject king Laman and the main verb deceive. If the prepositional phrase were not there, we would naturally expect “for this very cause hath king Laman deceived me”—that is, without the repeated hath. The repetition appears to be intended here, just as it is in the following passage:
In this case the original text repeats both the auxiliary verb were and the adverb also. The 1907 LDS vest-pocket edition removed the entire redundancy by deleting the first occurrence of were also. The 1911 LDS edition deleted only the verb were, leaving a partially redundant reading with also to continue in the LDS text. Of course, the original text here intentionally repeats were also because of the long intervening relative clause (“which were at the garden of Nephi and heard his words”). Such repetitions help the reader recover what has been initially stated. The critical text will restore such redundancies as the repeated hath in Mosiah 10:18 and the repeated were also in Helaman 9:11.
Summary: Restore the redundant hath in Mosiah 10:18 (“for this very cause hath king Laman by his cunning and lying craftiness and his fair promises hath deceived me”); a similar redundancy is found in Helaman 9:11.