In the real world, though, opportunities arise that neither &quot;a&quot; nor &quot;b&quot; take advantage of.<p>One of them is noted in the article...grey area product sources.  If &quot;b&quot; isn&#x27;t taking the time to find distressed inventory, there&#x27;s an opportunity for a middleman to do so, and undercut &quot;b&quot;.<p>There&#x27;s also some value added where the middleman has expertise or something to offer that neither &#x27;a&#x27; nor &#x27;b&#x27; has.  That could be better marketing (product photos, how-to videos), or better support (more lenient return policy, deeper technical support, etc), bundling multiple products together, niche sales, or something else.<p>Generally, successful middlemen find something missing between &quot;a&quot; and &quot;b&quot; and fill the gap.  Is it a war of escalation, where either &quot;a&quot; or &quot;b&quot; can react?  Sure...but typically middlemen can move faster.<p>Or, in short, they exist for a reason, and I don&#x27;t see that the internet age changed anything about that other than pace of change.