One of the purposes of LINQ is to make queries correct at compile time.

How many potential orderings do you have? You could do something like:

IEnumerable<Products> data1;
switch (orderByFieldName)
{
   case "ProductName":
   {
       data1 = nw.Products.OrderBy(p => p.ProductName);
   }
   case "ProductID":
   {
       data1 = nw.Products.OrderBy(p => productID);
   }
   // etc
}

Alternatively, I believe Marc Gravell has some code to produce an
appropriate expression tree from a property name if you really want to
go that route.