Why not just make the crop marks in InDesign.
Put a rectangle of fill none and stroke none on the master page around the page edge
There you have your crop marks in indesign.
But if you have PDF with Crop marks already on it why not just print from the PDF?
Why are you placing the PDF back into InDesign?
Getting crop marks isn't the issue, as I can do that using a variety of methods, including what you describe. In our case, the PDF is less work because we create individual PDFs of each object (business cards, in this case) to send out for proof and we'd rather use the handy built-in method of placing a PDF to a master of several cards instead of pasting or recreating each original on the master.
I guess I'm just wondering why a robust program designed for production printing such as this has an option for including crop marks in a PDF if the PDF isn't going to be accurate when placed back into a design file? I was hoping I made an error in my set-up somehow, which is still possible I suppose.
I can understand why you're doing it like that, in fact I do exactly the same thing but I never have any problems? How are you aligning them? I use math and the position fields. Could you supply a screenshot of what you do? Use the camera icon on the web interface to select and upload a previously saved image like this:
I do the same thing too, but when I import I change the crop option on the PDF to "crop" and remove the marks, dropping it into an ID template that has its own marks in the correct positions, or if for some reason I want to preserve existing marks I use step and repeat to position multiple copies, then relink the ones that should be different.