To check if a Dictionary has an specifique key, you can call the method [ContainsKey(TKey)](<https://msdn.microsoft.com/library/htszx2dy(v=vs.110).aspx>) and provide the key of TKey type. The method returns a bool value when the key exists on the dictionary. For sample:

var dictionary = new Dictionary<string, Customer>()
{
   {"F1", new Customer() { FirstName = "Felipe", ... } },
   {"C2", new Customer() { FirstName = "Carl", ... } },
   {"J7", new Customer() { FirstName = "John", ... } },
   {"M5", new Customer() { FirstName = "Mary", ... } },
};

And check if a C2 exists on the Dictionary:

if (dictionary.ContainsKey("C2")) 
{
   // exists
}

The ContainsKey method is available on the generic version [Dictionary<TKey, TValue>](<https://msdn.microsoft.com/library/htszx2dy(v=vs.110).aspx>).