At the moment my biggest bug bear with Id is fonts! I'll pick a pretty standard font which you see on just about every windows machine since 3.11, and it seems that it's not available on other systems, and for some reason Id didn't embed the font data for it. Then the print shop comes back to me saying the fonts missing!
When it comes to working with Id, it was actually one of the local print shops that told me that I should keep the photo components of the document in RGB, which also seems to match the general consensus of advice. Mostly I just use the original Adobe defaults for export from Id to PDF, they seem to work really well, so no point in buggering about with them. If a print shop has specific instructions for you then follow them.
I did a job for a support group that I go to, designing a banner that was going to be done on reinforced vinyl. I had been asking the manager to find out some of the technical details for what was required, and was being met with the usual blank look you get. A bit later I overheard one of the other users asking the reciprocal type of questions, again being met with that blank look. Fortunately he was the one doing the printing, so we got it sorted out PDQ between us. It was nice to just be able to talk about the technical stuff without an intermediary.
I think it's the fact that in many print places you pick up the phone to talk to them, and you just get a sales person, not a print technician, so the moment you start talking technical stuff the sales persons eyes just glaze over, you get that blank look, and they just come out with whatever bits of stuff that they have overheard at some point, just to get you to buy, and get you off the phone before you cause the head to self destruct in five seconds
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Alan