We output files at 175 LPI (Lines Per Inch) which is approximatley 300 DPI (dots per inch).
Any online proofs will be standard web resolution at 72 DPI and does not reflect how your product will print, i.e. proofs only show layout, not colour.
If we find any major problems with your files (example, wrong size, where you ordered 4×6 and you sent in 5×7, and the files do not scale proportionately), we may give you an opportunity to provide new files before we print. However, we cannot find every conceivable issue and you are responsible for your own files if they do not print the way you expect them to.