Blagging: As far as I can tell the term 'blagging' was originally coined to refer to celebrities who were able to get stuff for free. They wouldn't even need to ask for products and would simply be given things for free just for walking in to places, with other companies hunting them down to force their products on them.
This still occurs today, although to a lesser extent since things such as freebies in Oscar bags started being taxed (See Times Article). As celebrities are able to get freebies with so little effort, the term 'blagging' has over time moved away from celebrities and instead been redefined to refer to members of the public.
In this context 'blagging' refers to anyone who is able to achieve something despite not fulfilling the required criteria. For example if someone didn't revise for an exam and then passed anyway people may say they were 'blagging' it. If I was given access to the VIP lounge in a club it would also be used in this context.
Blagging can still refer to the act of getting something for nothing, but the word is given its meaning more because that person didn't spent any money (even if they spent a lot of time trying to get something for free, the meaning remains as the typical criteria is the act of spending money).
The flip side of the coin is when 'blagging' is banded about to describe people who are cocky or 'full of themselves'. This is taken one step further to describe con artists (e.g. "That second hand car salesman is 'blagging' them a bad deal"). The use of the term in this context devalues the meaning for those who are genuinely using 'blagging' for legitimate means.
Do you have a different Blagging Definition? Post it in the comments....