with new bct update to become a full member need 100 merits and i still have only 10 merits. What is the best way to earn merits
Its very simple,post some good quality posts then it will earn you some merits. 
That is the only way you can get or earn merit.If you are getting the merits in some other ways means you are abusing the system and you will get tagged by DT.
The problem is that people will not be motivated to give smerits to good quality posts because they rather choose to keep them as commodity. Would you give your last merits, when you need badly to receive some in return?
This system would work better imo if when you gave merits, you received a bit back, lets say 0.5 or 0.1 out of 1 merit given away.
Edit. It can be called a commodity, in a context, because has value. I would have made it this way: not linked to forum rank. Imo, smerit should be like a thank you, have no trace, no criteria, no stain and no self gratification and especially no pride.
Either way. Who cares? Let's see how the changes bring positive thoughts around.