Essential Edits can likely help with most non-fiction books intended for a general audience, but will only take the contract if at least one staff member has sufficient expertise in the topic to ensure quality work.
It is helpful if the client is clear on the type of editing required when shopping for an editor. If the consumer just says "editing" they might end up getting a copy edit (corrections for spelling, grammar, consistency, and so on) rather than the structural or substantive edit (what is working and what isn't) that they were expecting. Essential Edits always starts with a sample edit to assess the level of editing required so that an accurate estimate can be provided and that the client is clear on what level of editing they are purchasing. The Editors Canada site provides an excellent explanation of the different types of editing available: http://www.editors.ca/hire/definitions.html. (Not all editing services listed are available from Essential Edits.)
Ghostwriting—creating original text based on author notes—may also be available from Essential Edits if the topic is within area of the staff's interest and expertise. (This service is not available to students writing assignments, theses, or dissertations.)
Essential Edits provides a free guide to working with an editor which describes how to use Microsoft Word's Track Changes feature efficiently to keep costs and frustrations to a minimum.
Essential Edits staff are members of Editors Canada.