I was offered a free flight. I arranged to meet the chap at the airfield and he said on the phone "bring your headset and we'll go for a flight". I didn't want to be a timewaster and told him it was ok at this stage, but he insisted. I bought the share there and then I was so impressed
I would expect a flight once I had made a conditional offer (i.e. I offer you £xxx on the condition of a satisfactory flight test) and then offer to pay for the flight if the sale didn't go through.