public class CalculatorService : ICalculatorService
    {
        public int Execute(int a, int b, string operation)
        {
            Console.WriteLine("Received request: ({0}{2}{1}=?)", a, b, operation);

            int result = -1;
            switch (operation)
            {
                case "+":
                    result = a + b;
                    break;
                case "-":
                    result = a - b;
                    break;
                case "*":
                    result = a * b;
                    break;
                case "/":
                    result = a / b;
                    break;
                default:
                    Console.WriteLine("Our calc executed hara-kiri.");
                    Process.GetCurrentProcess().Kill();
                    break;
            }
            return result;
        }
    }

                        var res = calculatorServiceClient.Execute(a, b, op);
                        Console.WriteLine(res);

                    try
                    {
                        var res = calculatorServiceClient.Execute(a, b, op);
                        Console.WriteLine(res);
                    }
                    catch (ArgumentException exception)
                    {
                        Console.WriteLine(exception.Message);
                    }

            using (var calculatorServiceClient = new CalculatorServiceClient("WS2007HttpBinding_ICalculatorService"))
            {
                calculatorServiceClient.Endpoint.Behaviors.Add(new CustomEndpointBehavior());

                calculatorServiceClient.Open();
                
                // ... 

    public class CustomEndpointBehavior : IEndpointBehavior
    {
        public void Validate(ServiceEndpoint endpoint)
        {
            return;
        }

        public void AddBindingParameters(ServiceEndpoint endpoint, BindingParameterCollection bindingParameters)
        {
            return;
        }

        public void ApplyDispatchBehavior(ServiceEndpoint endpoint, EndpointDispatcher endpointDispatcher)
        {
            return;
        }

        public void ApplyClientBehavior(ServiceEndpoint endpoint, ClientRuntime clientRuntime)
        {
            foreach (var clientOperation in clientRuntime.Operations)
            {
                clientOperation.ParameterInspectors.Add(new OpParameterInspector());
            }
        }
    }

    public class OpParameterInspector : IParameterInspector
    {
        public object BeforeCall(string operationName, object[] inputs)
        {
            switch (operationName)
            {
                case "Execute":
                    VerifyExecuteParams(inputs);
                    break;
            }

            return null;
        }

        private void VerifyExecuteParams(object[] inputs)
        {
            if (new string[]{"+", "-", "*", "/"}.Where(x => x == (string) inputs[2]).Count() == 0)
            {
                throw new ArgumentException("Your operation should belong to folowing list: '+', '-', '*', '/'. Please verify and try again.");
            }
        }

        public void AfterCall(string operationName, object[] outputs, object returnValue, object correlationState)
        {
            return;
        }
    }