How can I purchase a property from the person who only owns a GPA

I am looking to buy a plot in Sant Nagar A Block Burari Delhi 110084. The owner of plot owns a GPA on his name. According to my knowledge/broker this area has only has power of attorney and Registration of property is not allowed. As Supreme court had given a judgement in 2011 that the immovable property can only be transferred via a registered sale deed so I want to know how can I legally buy a plot in this area. Moreover I have one more query. We also have a plot in other near by colony Sant Nagar B block Burari. Both the colony A & B block has been regularised and provisional regularisation certification has been given by Delhi Government. Both colonies are out of 895 colonies which were approved provisionally by Delhi Government. Which browsing online for information I got to know that Kehriwal Government passed a rule and now people can register their property with GPA, however broker is our area informing that is is not yet allowed in both colony, they say only few streets fall under Lal dora and property can be registered only for those. I have checked colony map and our plot and and plot I am going yo by part of colony map approved and ahwon as residential plot. So I want to know which information is correct? Your vaulable input will be appreciated.