It's like any working relationship - at first, you don't know them, they don't know you - and you have distance / time zones / language etc. Sometimes an upload or download is interrupted, or your clever folder system fools them, and you only realize when they don't return all the images (so count, verify, confirm numbers with them etc). Or they return files named in a slightly-different way from what you need to get them back into Lightroom, or stripped of metadata. What you thought were clear instructions could be misinterpreted, or you omit something that seemed completely obvious - to you. Eventually you figure them out and vice versa and you can just tell them "here's 1200 images, no time to say what pp they need, but get Sanjay or Vijaya on it as they always know what I like". But first time round you've thousands of images, you're sending them to another continent and to someone you've never met, and there's a deadline - what could go wrong.....