Purge your prose of allegory, alliteration, and analogy. A book should be judged, after all, as something bought by a customer, not as something written by a writer. This is excellent advice. In a world now overrun by mystery authors organizing and financing their own book tours, nothing will make you stand out like organizing and financing your own book tour. Give away doodads.
Pens are popular, as are sweets.
This is excellent advice. All agents have solid grounding in literature. The International Association of Mystery Agents requirements for membership call for, in addition to an MBA, an advanced degree in literary critique with an emphasis on objective, dispassionate judgment. All agents see more clearly than you do the artistic value of your manuscript, and all agents are utterly objective about it. The way you can verify this is to ask a random sampling of a dozen agents for comments on your manuscript.