Here we go again with the pdf prepress marks!

No we don't have specs on our website. Gets too complicated and "most designers" ignore the specs anyway. This is a frequent customer too. Told them time and time again. The size request has come in. Pdf file given comes in at 9.0833in x 11.5833in which I've determined to be 8.5 x 11 once cut. The size they want is 27.125 x 35. Where do you not see this as frustrating? My workaround is to create a rectangle @ 8.5 x 11 powerclip the pdf into it then size accordingly. Guess what?! Doesn't equate to 27.125 x 35!
Let's throw in another annoyance while we're at it. Total of 7 pdf files. First pdf is all raster, all others are combination with one or two lines of text out of place. Now I'm forced to open those in photoshop and save out as tif.
Another scenario is with files that are to be 18 x 24 coroplast signs. We can fit 10 of those on one sheet but if the files have the prepress marks we cannot. Still takes time to remove them all. I understand where they have there place but it shouldn't be the default way to make pdf's.

Any imposition software can place N-up on a sheet size of your choosing and do so to any of the "boxes in a PDF. So in your case, to the trim box if you don't want bleed. Or, they can clip at the bleed measurement (or one of your choosing) and remove the pre-press marks automatically. They will tell you the PDF's sheet size minus the trim marks. And one can load the PDF (or use a hot folder and automatic templates) and resave out without the marks and to the PDF sheet size. Or ...

I cannot imagine not having and using imposition software.

But I also have never used a print service that did not have the specs available to me. That going back to 1989.

Yes, but that's relative to the use. If it's for Prepress, it should have bleed and cropmarks.
If it's for signs, it's useful to know the final size of the sign, if it's not the same than the page size.
Using a powerclip means to use CorelDRAW for edit a PDF, but that could be a risk, since some things could change. btw you can crop the PDF using Acrobat also.