If so, that pilot ought to be sacked for overlooking 2 screws.
Facts:

• Demo unit - Compensated
  
• 2 missing screws - You claim that you checked everything yet you overlook the 2 screws as opposed to the Demo word on the receipt
  
• Duration in your care - Approx 50 days although we've been discussing it as 1 month or more than 1 month
  
• I do not have photo of rear lens, preferably dated 2nd May 2012. This proves nothing as dates can be faked, so its neither here nor there.
  
• You do not have photo of rear lens, preferably dated 6th May 2012. This proves nothing as dates can be faked, so its neither here nor there.
  
• You said you care how many have used the lens before you. You did not ask how many.
  
• You said it is your standard to take a photo of rear lens. You did not request for one.
  
• You indirectly accused me of duping. Directly accused me of being dishonest.
  
• Nikon did not take apart the aperture ring, it was already in that condition when you submitted to them for repairs.
  
• Dropping or knocking a lens do not 100% guarantee a scratch or dent. Experienced users can testify to that claim.
  
• To quote the exact words from the quotation, it went: RETURNED UNREPAIR AS REQUEST. IMPACT DAMAGE, WARRANTY NOT APPLICABLE. SCREW MISSING, APERTURE PROBLEM, REPLACE G1, G2, G6 LENS, AF CONTACT, G4-G5, G7 ASSEMBLY, QUOTED RM1,202.00.
  

Assumptions:

• Assume your elements groups weren't damage, I don't see why Nikon would con you.
  
• Assume the 2 screws are already missing while in my possession, I overlook that and you overlook that upon receiving it. In that case, I fail to see how 2 missing screws on the mounting can cause so much damage.
  
• Now you claim the same lens was submitted to Nikon for repair prior to this incident, with similar issues. Namely: Impact damage, screw missing, aperture problem, replace G1, G2 & G6 lens, AF contact, G4-G5, G7 assembly. If that was true, I fail to see how the lens was still operable while in yours and my possession.
  

Solution:
Now, I'm not sure what kind of solution you're looking for but what I can offer you is only peace of mind even if indeed said lens was submitted for repair prior to this. For you now know the cause of 2 missing screws weren't you.

This problem involves 3 party
1. Seller's friend that probably cheated at the 1st place
2. Seller, which is from my point of view is unable to accept the situation + a little bit of arrogance + SAFE TRADER
3. Buyer, who was sold on false information. EG: warranty.

Perhaps the seller is overprotective of his friend,
or he also didnt fully check the lens and bought from his
friend in order to make profit here (then refuses to admit that he was careless too),
Or he knew the lens was broken but decided to sell it anyway.

Nikon definitely proved that the lens was already damaged before it was sold, and the lens wasnt repaired.
What to do now? Seller's friend probably the one that knew everything right from the start.
So they should deal with him/her 1st to get further explanations.

Complicated.

New Update guys:

http://forum.lowyat.net/topic/2456093/+0&#entry53573988