When comparing quotes for interior design and typesetting, a HUGE issue to quantify is the charges for modifications to the text content after first pages have been typeset.
Traditionally called EA/AA (Editor Alterations/Author Alterations) these are CHANGES to the content at the request of the publisher, not mistakes by the typesetter/layout artist. (which are traditionally referred to as PEs (Printer Errors))
Almost all typesetters/layout artists charge for this work since it is additional time, sometimes substantial time, spent working on your project due to your changes. Charges may be billed by the hour, by the page, line, or word, or simply as a flat percentage of the overall per page rate or overall bill.
These charges are valid and normal, but you must realize they can be VERY substantial if you make extensive changes. You should understand what your exposure is before selecting a vendor. (see related tip The Cost of Changes)