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, on signage, bottles, windows, t-shirts, whatever. Output devices & their specs (esp. color profiles) change, industry-standards sometimes aren't, and many production shops use Adobe (& industry related) apps from 2013 - while designers (& their files) usually have "the latest, greatest" updates . . .

Time spent on conversions & "fix-it" charges at these 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 design intent, but appearing on signage/billboards, or cut vinyl, maybe embroiderers, and the more typical destinations - brochures/flyers/POP, the web, etc. Commercial printers, specialty item providers, daily/hourly e-mail/social media "appearances", weekly/monthly print publications - most print shops and/or marketing wonks, have no file submission wiggle room. If said vendor is desirable enough, they're very busy, and therefore, very scheduled ...
Plus (of course), always right ...

Aggravation has to be nipped in the bud . . .

$90-$120/hr. is the common range for charges, if said shop has to make "those changes" in-house, THEN deadlines become threatened (naturally). As a prepress/graphic design concern, WE are the responsible ones - not only for translating the designer's files (and/or, ours) to said production environment, but also for preparing the client for those "unforeseen" revisions (and, the associated delivery delays) . . .
Oh, yes - we've been known to "eat" said charges (even when we're just the messenger) . . .

What SHOULD save a designer's tush is the ability to see potential problems early - before the job even gets to the prepress proofing stage - e.g. explaining why the client's computer monitor "view" ("right here - THAT'S the green I want!"), or a PMS ink color vs. its' process color (CMYK) "match", won't look the same when "printed"  . . .
No commercial prepress shop wants to get involved in any explanations as to what's entailed in the world of color space/color profile translations, ink saturation/dot-gain coverage, plus any proofing vs. final print variations - but Flying Dutchman is built to be able to handle the occasional teaching atmosphere & the inevitable heartache . . .

Sometimes, the diplomatic effort necessary when trying to "improve", or "smooth out" the client's inconsistent grammar and/or writing style, can easily become counter-productive . . .
We know that those "helpful hints" can be less than smooth . . .

So, having a continued relationship with a client (you) should involve a help/trust factor - but, proofing perception snags ("press checks aren't free?"), "expert" (but non-tech) input from print salespeople (who may need an intervention), or pressmen having a bad day (press checks again), plus the "we've gotta catch a plane to Vegas on Friday" deadline, 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, as we keep costly surprises at bay - but, not being rusty (esp. technologically) really helps limit the scarring . . .

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