Legal Aspects in Selling Property of a Person Through Me

Hello, I am from Odisha. I came across a person who has around 1 acre of land in a prime location where land costs around 40-45 lacs per guntha (1742 sq.ft). Now I made a deal with that person that I will pay him an advance of Rs.5 lac and he will pass me the privileges of selling the lands on his behalf. This is kind of brokerage where I will make a bulk deal with him. As per the deal, I have to sell the one acre land to multiple buyers and he will take 35 lacs guntha from me. I can charge whatever to the buyer and that will be my profit. I expect to pocket around 5 lacs per guntha. Eg. Suppose I find a buyer who is interested to buy 2 guntha plot. The land owner will come to registry office to sell the plot. The buyer will pay me 80 lacs for 2 guntha land and I will pay the land owner Rs. 70 lacs and 10 lacs profit stays with me. The seller sells the plot, the buyer gets his money and I receive my cut. That's it. It will take me around 6-9 months to sell all his 1 acre plot. Now my concern is that what type of paper work should I do with the land owner? Would it be on a standard court paper? Any special clauses that I should have there so that he can't cheat or get me into trouble later? In case of any land related dispute, will the buyer hold me responsible or the actual owner? Please guide. Thanks a lot in advance :)