Let's draw a distinction between "shopowner" and "patron".
When you say "customer", which one are you talking about.
Patrons - those people who might purchase from your shop, do not have the option for PrintItAnyway.
Only Shopowners, purchasing their own designs have access to PIA.
Shapeways does not use PIA as an excuse to destroy your model.
They make every effort to produce your model faithfully, even if it fails.
For example, if you select an item in Red WSF and you select PIA, that does not excuse them to print it in Yellow.
If your item shows up in Yellow, you're well within your rights to ask for a reprint or refund, because that part of the process is controlled by them.
If however something BREAKS on your model, or otherwise falls outside of the design guidelines, then no, they're not obligated to re-print.