My general rule is that you should target your choice of writing seminars/workshops/conferences to your personal goals. If your goal is to publish fiction with a large commercial press, you should select instructors who have themselves published fiction with a large commercial press, who have been agents for fiction published with large commercial presses, or who have been editors for fiction titles with large commercial presses. If your goal is to publish poetry with a small press, you should select instructors who have themselves published poetry with a small press, or who have been poetry editors for small presses. If your goal is to publish non-fiction with a university press, you should select instructors who have published non-fiction with a university press, or who have edited non-fiction titles with university presses. If your goal is to self-publish a memoir and sell more than 10,000 copies, you should select instructors who have self-published a memoir and sold 10,000 copies. And so on and so on.
This may seem terribly obvious, but there are a lot of people out there selling "expertise" in things they have no actual experience with.
So, with the Murphy Writing Seminars, I would suggest evaluating how closely Mr. Murphy's writing and publishing experience matches with your writing and your goals. He has certainly placed poems with well-known literary journals, so if that's what you're looking to do, he may have very relevant experience for you.