Boil green beans in water to cover 2 minutes; drain. Plunge into ice water to stop the cooking process; drain again.
Combine green beans, lettuces, and bell peppers; set aside.
Combine flour and next 4 ingredients in a shallow dish; set aside.
Combine milk and buttermilk.
Dredge crabs in flour mixture, and dip in milk mixture. Dredge in flour mixture again.
Pour oil to depth of 1 inch into a Dutch oven; heat to 350°. Fry crabs 1 to 1 1/2 minutes on each side. Drain on paper towels. Cut crabs in half.
Toss together bean mixture and 1/2 cup red wine vinaigrette; place on serving plates. Arrange 4 crab halves on each salad and dollop each with shallot-dill mayonnaise. Serve immediately.