How do I see a virtual proof of the interior of my book

Unfortunately this is not currently available through Bookvault just yet - what you can do is download the files from our system once they have gone through our pre-flight checks. Check our guide out here on how to download and check submitted files.

Any cropping / margin or sizing issues should be apparent from this 

This would not highlight issues relating to font embedding, transparency or layering issues and would suggest getting a single copy of your book produced to check these things over.