The idea of suspended belief has never really bothered me because as a voracious reader, every time I pick up a mystery, thriller, science fiction or even a western to read I know I'm going to suspend belief.
Do you really think that each time Jack Reacher goes to any new town he's always going find someone that needs his help? An underdog, often a vulnerable female needing him to go up against a monstrous gang of bad guys he'll have to beat-up or better yet kill them all.
Remember, Murder She Wrote. We all laugh and say, I don't want to go to Cabot Cove Maine. Because in that quaint little beach town, that's the murder capitol of the world, I might find a body. Angela Lansbury/Jessica Fletcher always did.
But we always suspend belief to read the story. As writers, we try very hard to make our mystery world as real as possible so our readers will absolutely suspend belief and read our books. One of the major strengths of a mystery story.
To make our character's world as real as possible we research our character's job. If it's law enforcement or private investigation or newspaper reporter or international spy we try our best to make that job sound as authentic as possible. It helps tremendously if we have actually worked in the field we are trying to portray. The lingo of the field is especially important.
If our character is an amateur sleuth it often helps if that character has a love of cooking or bird-watching or quilting or something that we also do ourselves. It can add to the "reality" of our story.
If as a writer we don't have the job or hobby experience then research, research, research. Naturally, life experience or life knowledge can help. All can be used when writing and setting up the suspension of belief for our readers.
Something I try to do, in my book especially, is to include as much "truth" as possible. A "universal truth," as my mystery writer friend, Susan Rogers Cooper and I call it, is often a good thing to include. For instance, if my female character is to pack for a four day trip, she notes that she only has three clean bras that are really nice enough for the trip. So she either has to go buy a new bra or two, plan to wash one on her trip or pack one of her old "house only" bras. Almost all women can relate. It is so true. A lot of men can't relate but, men probably won't mention what he is packing in his book.
My main hope is when I do find a body someplace and write about it, you know I probably have not found a body our here in the Texas Hill Country but, you will believe me and suspend belief.