Photo and Line Art Image Problems

I have a print book on Amazon originally through CreateSpace. I uploaded the manuscript using a standard PDF file generated in WORD. It's a technical book heavy with illustrations both photo and line art. Over time using the same process through three updated files the results were printed proofs and books that looked great. I am considering using using a second source for printing and possible distribution. I first tried Dickinson Press dpdigitalbooks.com. I uploaded the exact same PDF file I used with CreateSpace. When I got the printed proof both photos and line art looked terrible, washed out. According to support there were two problems. First many of the images were color and needed to be B&W for a B&W book. Second I had to upload the PDF as PDF/X-1. I converted all images to grayscale. The only options for generating a PDF/X-1 were all expensive. I did find that PDF Creator will generate a PDF/X-3. From what I researched the PDF/X-3 should work. I uploaded the PDF/X-3 file and ordered another proof. The second proof looks as bad as the first.
Has anyone had problems with print on demand images looking bad? Is the PDF/X-1 file really that critical? I find this a bit odd considering I sent CreateSpace a standard PDF with color images for a B&W book with great results.

I like Michael's explanation. I read the blurb on PDF/X-1 and apparently PDF/X-3 is acceptable, just not in the US. There are no Kinkos in small town Iowa. There is one shop downtown that does more traditional printing. I'll check with them and see if they can make a compliant PDF/X-1. Considering that CreateSpace was able to do a great job with a non-compliant PDF makes me wonder what they do.

I just had a 'duh' moment. With CreateSpace you could upload either a WORD document or PDF for the book interior. It would not matter what PDF format I used because they convert it for me. In effect they did for free what some other printers charge as a service. I checked and it's the same with KDP Print. I'm thinking that for now I will just use KDP like I did with Createspace and order author copies for resale.