advocating for the preparation of a 706 could give the appearance of self-interest, so it is best that the decision comes from the executor, who should be informed of an estimated cost. There are not a lot of 706's filed these days and they should be prepared with the assumption that they will be audited (although that could be said for any return we prepare).
funny story, in probate an executor complained to the judge of a $7,000 bill for the 706--the judge reviewed the size of the estate and changed the bill to a percentage of value, which resulted in raising it to $50,000.