I am really very upset. On month July'13 one of my real estate portal back links increased from 68 to 93. but last week on August i found it decrease by 30 and now showing 63. What is the problem really I failed to understand.
I agree, check the individual links. Don't depend on what a search engine shows you. If the link exists then it is known by all the search engines. Whether the link counts or not, or how much the link counts, is an unknown. Bottom line is keep an eye on the rankings not how many links a search engine shows you. Good luck.
Don't depend on what a search engine shows you. It is only a sample, it does not show you ALL your backlinks. It is and has ALWAYS been a sample. If you register your site at Google Webmaster Tools they may show you more. But even there they do not show you a complete list.
The links to your site section of Google Webmaster Tools is a great starting point for an investigation as it shows a significant amount of your site’s inbound links.
Do not try to extract meaning from the links:domain results. There is no meaning to the links shown. Historically, the results shown there were and are an incomplete SAMPLE. They showed links that counted to your ranking. They showed links that did not count for your rankings.
Because those results are not useful for SEO purposes, I advised you to keep an eye on the rankings not how many links a search engine shows you. Because the links the search engine shows you are incomplete and do not give you an idea of whether they are helping you or not.