Moq: Specifying return values as part of expectations

I'm new to Moq and learning.

I need to test that a method returns the value expected. I have put together a noddy example to explain my problem. This fails miserably with:

"ArgumentException: Expression is not a method invocation: c => (c.DoSomething("Jo", "Blog", 1) = "OK")"

Can you correct what I am doing wrong?

[TestFixtureAttribute, CategoryAttribute("Customer")]
public class Can_test_a_customer
{
    [TestAttribute]
    public void Can_do_something()
    {
        var customerMock = new Mock<ICustomer>();

        customerMock.Setup(c => c.DoSomething("Jo", "Blog", 1)).Returns("OK");

        customerMock.Verify(c => c.DoSomething("Jo", "Blog", 1)=="OK");
    }
}

public interface ICustomer
{
    string DoSomething(string name, string surname, int age);
}

public class Customer : ICustomer
{
    public string DoSomething(string name, string surname, int age)
    {
        return "OK";
    }
}

In a nutshell: if I wanted to test a method like the one above, and I know that I am expecting back an "OK", how would I write it using Moq?

Thanks for any suggestions.