The Diff snap evaluates based on the exact values in each column of the incoming records. If a record exists in the Original and New inputs, but has a different data type in a field, then it will be evaluated as a Modification. For example, if a value is stored as “$50.31” in one document and 50.31 in another document, these are different values and should be marked as a Modification.
The best way to solve this is to standardize the inputs in a Mapper snap before the Diff to align the data types of the inputs. For currency, parseFloat() will probably help.