...eautocatalog.com is a parts wholesaler. As an aid to their customers (the retailer), they've created (or more likely had created for them by someone else) a web application for use by the retailers.

Kinda like the old days when say, Moroso would print their catalog with a blank white space on the cover so that a local shop could have "Pete's Speed Shop presents" on the catalog.

As always, retailers are free to set their own prices. I can't speak to the technical aspect of how this is done, but I'm sure it's not difficult if you're a techno-geek.

Bottom line is that I've seen at least 4 (maybe more) online retailers that use eautoparts'com's cataloging service. That by no means that all of these retailers are in any way affiliated, other than they use the same web engine.

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Another theory: All of these retailers have their own suppliers for various parts, and eautocatalog.com only sells/services the web application which they've developed.