True.Here local mechs only fleece you its better to take it to some good SC even if it is 100 kms away...i learned this the hard way .

Finally got the bike repaired....the valves were fine no damage....the culprit was carbon deposit that led to the valve being open hence the compression loss.

They gave the head part to a lathe to "reseat" or something.The top part of the piston was black they scrapped it off with a screw driver.

What could be the reason for this excessive carbon build up? for the last 10000kms only i use mineral oil for the most part i was on motul 300V only.Even with mineral oil i change it at 1500kms.could it be the petrol

It cost me Rs 445....i did not change the oil as it was just a few days old and the head mech too said its ok .

If your bore and piston are in good condition then it could be oil leaking through Valve stem seal....because you say the carbon build up prevented the valves from seating properly, this seem to be the likely cause..I hope they have changed the stem seals also..
Good luck Ride safe.