var firstName = person.FirstName;
if(nameChecker.ConfirmName(firstName))
{
  ...
}

var age = this.GetUserAge();

var myList = new List<Tuple<string, int>>();

List<Tuple<string, int>> myList = new List<Tuple<string, int>>();

A>YepIAmSpecifyingTheConcreteTypeExplicitly myObject = service.getMyObject();
A>

A>MyEliteService service = ....
A>service.getMyObject(); // вот тут возвращается null
A>

A>int iThinkThisShouldBeIterable = service.getSomething();
A>foreach(int x in iThinkThisShouldBeIterable) { ... }
A>

A>Напишите своими руками аналогичный пример и вместе посмеёмся

        public override FrameworkElement CreateCell(C1FlexGrid flex, CellType cellType, CellRange range)
        {
            var cell = base.CreateCell(flex, cellType, range);

            if (cellType != CellType.Cell) return cell;

            var notes = dataTable.BodyRows[range.Row].Cells[range.Column].Notes;
            if (!string.IsNullOrEmpty(notes))
                ToolTipService.SetToolTip(cell, 
                                          new TextBlock {
                                              Text = notes,
                                              TextWrapping = TextWrapping.Wrap
                                          });

            if (dataTable.BodyRows[range.Row].Cells[range.Column].IsReadonly)
                ((Border) cell).Background = new SolidColorBrush(Color.FromArgb(0xFF, 0xF5, 0xF5, 0xF5));

            if (dataTable.BodyRows[range.Row].Cells[range.Column].IsRowHeader)
                ((Border) cell).Background = new SolidColorBrush(Color.FromArgb(0xFF, 0xEA, 0xEA, 0xEA));

            return cell;
        }

   Text = notes,

For example, suppose you did something like this:
    var distributionLists = MyEmailStore.Contacts(ContactKind.DistributionList);
Suppose the elided type is DataTable. 
Is it important to the reader to know that this is a DataTable? 
That's the key question. Maybe it is. 
Maybe the correctness and understandability of the rest of the method depends completely on the reader understanding that distributionLists is a DataTable, and not a List<Contact> or an IQueryable<Contact> or something else.

A>>2. Ну не делайте же вид, что пишете код в ноутпаде В этом сценарии студия вам сразу покажет, что в этом месте есть проблема.

MyService myService = ...;
myService.performTrickyAction();

var myService = ...;
myService.performTrickyAction();

var distributionLists = MyEmailStore.Contacts(ContactKind.DistributionList);

DataTable distributionLists = MyEmailStore.Contacts(ContactKind.DistributionList);
или
List<Contact> distributionLists = MyEmailStore.Contacts(ContactKind.DistributionList);
или
IQueryable<Contact> distributionLists = MyEmailStore.Contacts(ContactKind.DistributionList);

YepIAmSpecifyingTheConcreteTypeExplicitly myObject = service.getMyObject();

MyEliteService service = ....
service.getMyObject(); // вот тут возвращается null

int iThinkThisShouldBeIterable = service.getSomething();
foreach(int x in iThinkThisShouldBeIterable) { ... }

var list = GetList();
list.Add(1);
list.Add(1);

“Overuse of var can make source code less readable for others. It is recommended to use var only when it is necessary, that is, when the variable will be used to store an anonymous type or a collection of anonymous types.”

"I agree with Alexander. Var should only be used for anonymous types. It was designed for anonymous types and for use with LINQ. Using var to implicitly type local variables is not good practice and makes code more unreadable."

"After reworking some code and using var wherever possible, I can't say it has provided any benefit and at best obfuscates meaning in most situation."

"I really am having a hard time to read code with too many vars — it's just a reduction of information. While you may say that it "forces" devs to go with better variable names, I'd still opt for explicity typing *and* good variables (and people who don't care will still use bad naming schemes)... "

"Before var existed, was anyone in the community thinking "my code would be so much more readable if only I didn't have to type all my local variables"? No, of course not. It was pretty much invented only to support Linq. The fact that it can be used for non-anonymous types doesn't mean it should."

int var4 = ExampleClass.ResultSoFar();