I often get sample files from clients to use in building import routines; about 90% of the time i then have to fix the routine because the actual run-time files are different from the samples provided. Some of it is due to formatting issues, but often i find that requested business rules cannot be applied because the data is unsuitable.

For instance, setting a call date on newly imported records to 2 business days after the Ship date listed on the file; but the ship date field on the file is always blank.

This is only one example of the kind of data inconsistencies i see every day. If i had to work in a data-obfuscated environment, it would be impossible to get things right the first time (up to 100% from 90). I, for one, don't find the idea of doing extra work to make my job even harder particularly appealing.