First, I would be amazed if any reader was able to get this example working because it requires that you type hundreds of lines of code across multiple files before you can even begin testing the example out. Second, I think it would be helpful if someone at Wrox published the correct steps to get this working.
Here are a few errors:
On page 479, step 3 doesn't list all the "using" statements required for the code to work in Shopping.cs. The file in End\Chapter13\Shopping.cs does have the required using statements, but it also has this line, which is a little strange for C# book:
Also starting on page 479, the CartItem class declares a property named _lineTotal. This property serves no purpose; its value is set in the constructor, but it's never used anywhere.
In the middle of page 482, this line:
_items(ItemIndex).Quantity += 1
items(ItemIndex).Quantity += Quantity