NOTE: While proofreading is a service I do offer, it is on a case-by-case basis after an evaluation of the manuscript and the mutual decision that the work is ready for this service.
This kind of editing is the final polish before publication. It is designed to catch all those pesky errors that annoy readers while ensuring your manuscript is completely polished. The editor will go through the manuscript line by line, looking for any errors that might detract from the professionalism of the work. This does not check phrasing, mechanics, consistencies, plot errors, or facts. If a work needs that deeper editing, copyediting would be a better service. However, if the manuscript just needs a final cleanup, proofreading would be appropriate.