Ah-h-h, the Prepress Department . . .

This is probably the most nebulous, and therefore the most dangerous area in the art of putting ink/toner on paper, signage, bottles, windows, t-shirts, whatever. Output devices & their specs (esp. color profiles) change, industry-standards sometimes aren't, and many production shops have Adobe (& industry related) apps from 2012 - while designers (& their files) usually have "the latest, greatest" . . .

Time spent on conversions & "fix-it" charges at output facilities (vs. the estimate) can escalate quickly . . .

So, Flying Dutchman has to be very flexible in order to cover all output scenarios (the same basic job, but going to cut vinyl, embroiderers, signage/billboards, flyers, the web, etc). Commercial printers, specialty item providers, weekly/monthly publications - most have no file submission wiggle room. If said vendor is desirable enough, they're very busy & therefore very scheduled - and, of course, always right . . .

Aggravation has to be nipped in the bud . . .

$75-$90/hr. is the common range for charges, if said shop has to make "the changes", plus deadlines then become threatened (of course). As a prepress/graphic design concern, we are the responsible ones. Not only for translating the designer's files to the production environment, but also preparing the client for any unforeseen revisions (plus, delivery delays) . . .
And yes, we've been known to "eat" said charges (even when we're just the messenger) . . .

What CAN save any designer's tush is the ability to see potential problems early in the proofing stage - e.g. explaining why a PMS color vs. its' process color "match" won't look the same when printed (as opposed to the client's computer monitor "view") . . .
No one wants to get involved in detailed explanations as to what's entailed in said world of color spaces/color profiles, ink saturation/dot-gain, proofing vs. final print limitations, but . . .

Plus, the diplomatic effort necessary in explaining why the inconsistent grammar/writing style of the client may need to be edited, can easily become "counter-productive" . . .
We guarantee that things can get nasty . . .

So, having a continuing relationship should help - but, proofing perception issues ("can't we do a press check?"), non-tech sales people needing interventions, pressmen having bad days (press checks again), plus the "we need to be on a plane to Vegas tomorrow" deadlines, may all rear their ugly head . . .
Sometimes, even a sense of “what are you trying to pull?” might emerge (from either side) . . .

Sincere smiles, and the "hand-holding" function will always be with us, keeping costly surprises at bay - but, not being rusty (esp. technologically) really helps limit the scarring . . .

We ARE sincere (and yes, the Truth can hurt) . . .