You and @ tintin1 both are right. Point taken.
I don't argue with you guys on taking along an expert with you, but that person has to be trustworthy and shouldn't have a hidden motive. In my case I took an expert mechanic, whom I knew for many years. Not to offend anyone but he was a Hafiz-e-Quran and namazi/perhaizgar, unlike myself. His father was body shop Supervisor of a 3S dealership, and had been very cooperative with me for paint job of my two cars in the past. He took time and went everywhere with me. He didn't ask for any compensation. I had asked him to take care of all the mechanical work once I bought the vehicle.
This expert mechanic rejected a number of vehicles that we saw on one pretext or the other. He would keep quiet most of the times and wouldn't tell me much. On my repeatedly enquiring he would ask me to drop it due to the potential troubles. I remember clearly that once he rejected a Surf by saying that it needed a new engine, however the current engine of the vehicle wasn't even started. Eventually I got fed up and asked him to get me a good vehicle himself. Soon after he took me to Murree and showed me a heavily beaten up LJ79. The owner had excuses for all the breakdowns. But the asking price was too low. My expert mechanic told me that we can easily bring it to a showroom condition because it was all 'genuine'. I got tempted. Gave 100 thousand rupees as advance. Very next day they started pressing me for full payment. I stressed on checking papers. My expert started misbehaving, which was very strange for me. I ignored his rude behaviour but checked papers myself. As suspected there was a problem with issuance of duplicate number plates. After lengthy arguments I managed to get back 50 thousand rupees only. And parted my ways with my mechanic.
Then I learnt that having an expert by your side is important but you mustn't blindly trust anyone. Even your friends and cousins have certain biases towards the vehicle brands and models they own. So I thought to apply own mind and common sense also.
Hope I have cleared my point.