One: which level of work the figure covers
The professional bodies define the levels in terms specific enough to compare. Developmental editors deal with content, organization, and genre considerations. Line editors work at the sentence or paragraph level, correcting errors while concentrating on the language and style. Copyediting covers spelling, grammar, usage, and punctuation, along with checking cross-references and preparing style sheets. Proofreading comes among the last stages, checking for typographical errors and formatting mistakes.2
A quotation that says editing without saying which of those is being quoted has not answered the question. Editors Canada records the boundary from the other end, stating that proofreading is not a substitute for editing.3
Two: the unit, and therefore who carries the risk
Four units are in use, and the published rate survey reports figures for each.4 A per-word price fixes the author's total before the work begins and leaves the editor to absorb the chapters that turn out to be difficult. An hourly price does the reverse. A per-page price is a per-word price with an assumption about page density built in. A project fee is a per-word price with the arithmetic already done.
None of the four is more honest than the others. They allocate the same risk differently, and knowing which one is on the table is what makes two quotations comparable.
Three: what the figure was calculated from
A price produced from a ten-page sample is an extrapolation. Later chapters written under different conditions can be denser than the opening, and a figure that assumed otherwise will be revisited.
A price produced after reading the whole manuscript can be held to. Asking which of the two a number is costs nothing, and the answer changes how much weight the number carries.
Four: the schedule, and what happens if it moves
The Editorial Freelancers Association's guide for new authors records that rush work commands higher rates, and that an editor needs adequate time to edit a complete manuscript.5 Those two facts travel together. A date agreed before the whole manuscript has been seen carries the same uncertainty as a price agreed the same way.
The quotation should say what happens to both if material arrives late. That is not a trust question. It is the term most likely to be tested.
Five: what comes back
A copyedit should return three things: the edited file, the queries raised, and the style sheet. The style sheet is the document authors most often forget to ask for. It is also the one that makes the next manuscript cheaper, because it records every decision the chosen style manual did not settle. Building it is part of the definition of the work in both professional bodies' terms.23
What the five together let an author do
Three quotations that each state a level, a unit, a basis, a schedule, and what comes back can be compared on a page. Three quotations that state only a number cannot be compared at all, and an author choosing between them is choosing on tone of voice.
The EFA's guide adds the checks that cost nothing: asking what comparable work an editor has done, and asking previous clients. It also notes the limit of a sample edit, which can help evaluate copyediting or line editing but cannot capture developmental work, whose scope is too large to show in a few pages.5
EditFast quotes on the whole document rather than on a sample, and states which of the four levels the figure covers. The style sheet comes back with the manuscript. Estimates are free and carry no obligation, and everything a client sends is treated in confidence, including unpublished manuscripts, business documents, and correspondence. What the four levels cover and what a full manuscript comes to are both published.
An author who asks all five questions will occasionally be told an editor cannot answer one of them yet. That is a useful answer too, and it is different from not being told.