public ActionResult AddCustomerLinkToDB(string IsSeleted)
{
   string selectedCustomer = IsSeleted;
   return View();
}

@using (Html.BeginForm("AddCustomerLinkToDB", "Admin", FormMethod.Post))
{
    <table class="table table-bordered table-hover">
        <tr>
            <th>Customer ID</th>
            <th>Customer Name</th>
            <th>Select this user</th>
        </tr>
        @foreach (var item in Model)
        {
            <tr>
                <td>@item.Id</td>
                <td>@item.Name</td>
                <td>@Html.RadioButton("IsSelected", new { id = item.Id })</td>
            </tr>
        }
    </table>
}

public class ViewModel
{
    // since the CustID is numeric, I prefer using 'int' property
    public int IsSelected { get; set; }

    public List<Customer> Customers { get; set; }

    // other properties
}

@model ViewModel

@using (Html.BeginForm("AddCustomerLinkToDB", "Admin", FormMethod.Post))
{
    <table class="table table-bordered table-hover">
        <tr>
            <th>Customer ID</th>
            <th>Customer Name</th>
            <th>Select this user</th>
        </tr>
        @foreach (var item in Model.Customers)
        {
            <tr>
                <td>@item.Id</td>
                <td>@item.Name</td>
                <td>@Html.RadioButtonFor(model => model.IsSelected, item.Id, new { id = item.Id })</td>
            </tr>
        }
    </table>
}

[HttpPost]
public ActionResult AddCustomerLinkToDB(ViewModel model)
{
    int selectedCustomer = model.IsSelected;
    // other stuff

    return View();
}