Prints with Moire from print shops

Hi all

I suspect I already know the answer, however I want to make sure I don't miss a thing before responding to the customer.

When photos are exported and sent to various print shops, some return the very same image with Moire in Moire-critical parts of the image whereas others return a perfect print. Is there any way I can influence this or is this just 'bad luck'?

Of course, Moire is checked before and though there is some Moire in some locations there is no Moire in this location at 1:1. However, it's a killer: a small checked shirt.

Thanks

McL