When searching for backlinks using link or links query i get different number of results. why is that so ?
This is due to how hyperlink is displayed on the web page; the best method to view your backlinks via Google is to use Google Webmasters Central. As for competitor links unless you use the linkdomain: search operator in Yahoo! and go through thousands of non-true backlinks you'll never get a fully accurate report; yes all those tools, software suites, etc are liars!