When buying a house from the owner directly, what must be done to insure that the deal is clean and legal?

See the assets of the property papersTrack property documents if there is more than one buyerInquire about the property to make sure it does not have any mortgage or booking and otherInquiry about real estate registrationInquire about the property in the government agencies affiliated to the property to view the licenses and all the papersPrepare a purchase contract with a lawyer to ensure that all rights are proven

Make sure there is No Lein on the house and its under his/her name and everything is clear on the papers. So, there shouldn't be any issue at all when transferring documents under your name.

You dont want to buy it through a broker, you have to check the morgage of the house if any and you need to make sure tha you are buying it from the owner of the house.