Without a fuller context, the writer seems to be referring to a current situation [it is difficult to find a new job ] rather than to a past one.
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eagernessI wouldn't have left my job if I had known how difficult it is to find another one.Backshifting is always correct. was is therefore also correct. In fact, that's what I would have used. But the author used is to indicate that it is currently true that it is difficult for him to find another job. I
CalifJim It suggests that he is currently in the process of looking for a new job.Good point!