Let us assume we have this WCF Service definition
[WebInvoke(UriTemplate = "/clients",
    BodyStyle = WebMessageBodyStyle.Wrapped,
    Method = "POST")]
ClientDto Save(ClientData client);
Where ClientData is as follows:
public class ClientData
    public int Id {get; set;}
    public string Name {get; set;}
Now, let us write a load test with JMeter. Start JMeter

Add a new "Thread Group", and inside that thread group add an "HTTP Request"And add all the attributes of the URL in http request:
So add the server name, and add the method: "POST", and add the path to the message

In order to Post data to the service, we should add the "Content-Type" attribute to be json

We can do that with "HTTP Header Manager"
So, Add HTTP Header Manager,
Addd attribute: "Content-Type" and set its value to "application/json"

Come back to the Http Request and add body part to be the data we want to post

As you can see the json object we are sending match the parameter we should send to the service.

If you run the JMeter now, it will submit those values to the service, for one time.

We want to call this service many times , and each time have different parameters
So first let us go back to the "Thread Group" and configure how many times we want to call this service:

Add the following:
"Number of Threads (users)": make it 100, which means JMeter will imitate 100 clients calling this service.
On the second parameter "Ramp-Up Period (in seconds)", add 5 , which means these 100 called will be in 5 seconds.

The second step is to allow JMeter to read the parameters to the service from a file.
The parameters we want are the json object we are submitting to the service.
So, let us go back to the Http Request, and modify the body to have parameterized values.

 so change the value:

{"client" : { "Id" : 3, "Name" : "John Smith"}}

to the following:
{"client" : { "Id" : ${client_id}, "Name" : ${client_name}}}
As follows:

JMeter allows to add CSV file to be the input of parameterized test.
So, let us add "CSV Data Set Config"

Add the following parameters:
Filename: is the path to the location of the file.
Variable Names (comma-delimited): is a comma delimited of variables we want to substitute, which is in our case client_id, and client_name.

Now we are ready to run the JMeter, and check the load.
But we can measure that from Jmeter itself.
For that we want to show the result in a table.
So, add "View Results in Table"
And finally , just run the Jmeter, and you will see results similar to this.