Not every print service provider creates proofs of individual pages. Some may show you imposed proofs, which serve a dual purpose: You can check page content and color, and you and the print service provider can check for correct pagination (page position as a result of imposition). When viewing page proofs, you should check for the following:
Correct size. Make sure the page dimensions are correct.
Bleed. Make sure there is adequate bleed. If images must bleed, make sure they don’t fall short.
Image area. Make sure no artwork or text falls too close to the trim edge or interior spine. Such artwork will be at risk of trimming out or disappearing into a fold.
Correct fonts. Check to make sure text intended to be bold or italic ...