Process to buy an open file plot.

I have decided to buy a plot in a private housing society (city housing). The property agent says that it is an open file , he has the file so he owns it and all dues are paid. How can i verify that he is the real owner of this file, and has the authority to sell this plot. What should be the complete process to buy this plot and transfer it on my own name. This is the first time i am purchasing a plot and i want to verify everything related to this to avoid fraud. Please guide.