1. Ask your seller to get the land vacated first and hand over vacant possession to you
2. if you wish to enter into some transaction with the owner but fear that the neighbour who is growing fruits etc on the land, would not vacate, then I suggest that you enter into a Memorandum of Understanding with the owner in which it will be agreed that part consideration will be paid on signing of MOU and balance on registration of sale deed and hand over of vacant possession to you
3. impose a condition in the MOU that within x number of days of signing the MOU, the owner has to obtain vacant possession of the plot from his neighbour. If he fails to do so then you can terminate the MOU and demand refund of your token money
4. never enter into any sale deed without securing vacant possession of the plot. Who knows the neighbour may turn hostile and refuse to vacate. The owner would sell the plot to you, accept the consideration and move out. You will be left in a lurch if you have the headache of getting that neighbour vacated from the plot
5. no affidavit or any other document should be accepted by you from the owner on the premises that the neighbour has sworn in an affidavit to vacate the plot. its of no use. put the entire onus on the owner to secure the vacant possession of the plot
6. in fact i suggest you keep some balance money payable and pay that to owner after a week or so of registration of sale deed