Duplicate postings don't work anymore

Recently I got a question from a recruiter:

I have been a long time user and fan of your website. However, I have recently renewed several ads and I am experiencing some very slow indexing times to the partner sites. Normally, our response is very good and the postings seem to index daily. This time things seem to be taking much longer. Some of these renewals were posted on the 6th and are still not indexed on the partner sites. I am sure this is why our response has been so low. Have you changed something or can you give me an explanation on the delays so I can plan accordingly if this is a permanent change.

I really like your site and would like to continue posting to the job boards through it but need to know that when I post they will be indexed. We are currently contemplating as a management team whether to spend the money and use a pay service like monster and I really don’t want to have to go that route as the results there have not been any better than with your service when it is correctly indexing jobs. Please advise.

Here's my answer:
1) You posted LOTS of duplicates.
It worked for you in the past, but most probably won't work well in the future. That's why:

Reason #1: Duplicate postings not end up in search results

indeed.com and simplyhired.com fight duplicates&spam.
Your postings are indexed by indeed.com. In fact, PostJobFree postings are indexed by Indeed.com every two hours. But in order to see all your postings you need to click "repeat your search with the omitted job postings included." link.
Prompt indexing does not guarantee that duplicate postings will end up in default search results of job seeker.

Job seekers don't like duplicates, so job search web sites don't show duplicates.

Reason #2: Duplicate postings may be deleted

In the nearest future at PostJobFree.com we are going to suppress duplicates/spam.
If you continue to post lots of duplicates then chances are that you won't be able to make many postings on PostJobFree.com at all.
The more duplicates you post -- the more job seekers will click "Report Spam" button on your postings -- the less postings you will be able to make daily.

2) Here's what you can do to improve your job postings visibility:
Think less about gaming job search web sites and more about what job seekers are looking for.

What would job seekers like to see and what -- not to see?
In the end job search web sites try to please job seekers.

If you want to post the same job posting into different locations --
post only one job posting, but mention all locations in the body of
job posting.

You may also write different job postings for different locations
(even if they are in essence the same).

See also: How to avoid duplicates with multiple postings