Btw. Blogs start getting the same problem
. People start using social media platforms more and more for things that used to be blogged. Some even asked the questions if blogs are going to die. Nope, they will probably not anytime soon, but stuff where blogs were not the best choice to do it in a first place, will be replaced by things that are better suited for it and blogs will be used for what they are still best for, just like forums.
So, back to datafeeds.
I did not elaborate on the use of web services and the problems with real time data feeds in my first comment and some people who don't know about those kind of things might have a problem with understanding that part of my comment.
APIs (in form of a web service or not), allows to get real-time data for a small set of products or even specific products. In case of CJ, real-time as in the information CJ has for the product at that moment. If the merchant did not update the feed at the CJ network, the information could still be wrong.
Real-time datafeeds as in pulling the feed with current information (and not from whenever a data feed file was the last time provided) still has the problem that you get too much data back and still have to do the full processing on your end.
Since merchant provide the feed though, is the possibility of errors and problems with the feed somewhat smaller, since the network as middle man who is in some case causing the problem, is out of the loop.
If the real-time interface allows filtering of the results down to a very small set of products or even individual products, we start calling it API and not FEED anymore. A simple filter by department/category or type of product is sometimes an option, but still returns more data than you need. This adds to the overhead for transfering and processing the data and makes it often inefficent to use that kind of interface for real time calls on the fly when a user hits a page on your site. That on the other hand causes issues for you and the merchant if you have a large amount of traffic and calls to make.
I hope that clarifies things a bit more