You should implement the IEnumerable interface (CarBootSaleList should impl it in your case).
http://msdn.microsoft.com/en-us/library/system.collections.ienumerable.getenumerator.aspx
But it is usually easier to subclass System.Collections.ObjectModel.Collection and friends
http://msdn.microsoft.com/en-us/library/system.collections.objectmodel.aspx
Your code also seems a bit strange, like you are nesting lists?