Here you go Nirmaan, this is how basically they do BC and SC checks(Taken from OP6 manual bible)
Final determination of eligibility for processing(now done at CIO)
Where documents are reliable and information is clear, consistent and well-supported the final
determination of eligibility can be made quickly. Where this is not the case, the final determination
of eligibility will be more involved.
Exercising diligence while making a final determination within the ideal timeframe means the
determination will be a paper review of the application and supporting documents. Visa officers
must apply their local knowledge to the application and documents to determine eligibility.
Documents lacking sufficient information about the employer, or containing only vague descriptions of duties and periods of employment, should be given less weight. Descriptions of duties taken verbatim from the NOC should be regarded as self serving. Presented with such documents, visa officers may question whether they accurately describe an applicant's experience. A document that lacks sufficient detail to permit eventual
verification and a credible description of the applicant's experience is unlikely to satisfy an officer of an applicant's eligibility.
Interviews, verifications of the authenticity of documents, site visits, investigations or seeking
clarification from applicants constitute processing. These activities may be undertaken to
determine if applicants meet the minimal requirements, can be awarded points for the selection
criteria or are inadmissible.
Once processing begins, officers will review the application against the minimal requirements and
the selection criteria for FSW. Visa officers are also required to approve or refuse FSW
applications according to the requirements of the Immigration and Refugee Protection Act (IRPA)
and the Immigration and Refugee Protection Regulations (IRPR).
In cases of refusals, this means an applicant fails to meet the minimal requirements, is not
awarded sufficient points or is found to be inadmissible. As applicants may specify more than one
NOC code in their application, failure to meet the minimal requirements for an occupation on the
MI list will not necessarily result in refusal.
My Own words:
In today's net age.......the VOs don't have the time and money to spent on BC.
There are various softwares available to use on the internet like SnoopStation.com for US, 190.com for UK and something like Khoj.com(not sure abt the last one) for India.
They charge a nominal fee and especially the indian site helps to get you the age,educational credentials,marital status and many more info by collecting the various info from various other sites.
The report for an individual is generated witin seconds, hence saves valuable time and resources.
I hope this info is useful!!!! The above are just my views and I can be wrong
, as one window of this thread is always open on my workplace 
