This is probably old news to many, but could be helpful to others. Looking for commentaries by simply using text such as "Mark" will produce many false positives (all titles whose author's first name is Mark or that refer to a mark as in "hitting the mark").
Now all commentaries are catalogued by subject type as such and under their book names. One however can be daunted by the fact that the subject headings in the catalogue are difficult to remember and format properly. For instance, for Genesis, the subject heading is Bible. "O.T. Genesis--Commentaries," and will only work if the spaces are put or omitted at the proper spots. Cumbersome.
What is more, as observed elsewhere, some commentaries subject headings require even more specification with the corresponding potential for error, like "O.T. Genesis 1-11--Commentaries."
Solution:
Using subject:Genesis will find all subjects headings that have "Genesis" in it (or Matthew, Mark, etc.). This does not include authors' names. Combined with type:commentary, you will find all the commentaries on the book you are looking for. In the tries I did I found no false positive.
You can use that in searches. For instance, to find all commentaries on Mark in which the discussion of Mark 10:30 speaks of farms or land, you can do something like this:
