When we bought the 172, we found the seller, agreed on a price based on the premise that the aircraft would be "as described" and pass a pre-buy inspection, no deposit. Seller transported the airplane to our shop of choice for prebuy, which came out as expected, top-shelf, we paid the prebuy and fuel cost for transport. We then flew commercial to inspect the airplane in person and test fly it, it all checked out as described and advertised, deal was closed on the spot.
If your seller is legitimate, they won't throw roadblocks in front of potential buyers, they will do what is reasonable to encourage them.
As for the actual sale transaction itself, we had pre-established an account with the sellers bank, and placed our funds in there. Once we agreed to the deal and shook hands, we went to the bank and had them transfer funds from our account to his, and the banks notary witnessed the receipt and deed of sale. Easy as pie.