There are a few difference
1. the build quality of the first copies isnt as good as the original ones
2. each plug has a batch number on the box,u enter the batch number n u can c the specs n fitment of the plugs
3. couterfit plugs start cauging problems like wornout tip,misfires etc..
4.there a v clear cut difference in the prices of original n fake plugs,eg ngk fuel tip plugs which are for the axio,the original ones are above 1.5k/plug whereas the fake first copy ones are easily available for 800-850rs.
n ull find out when ur tip erodes out after 5-6k kms
these are some of the idenfitications there are many more as well.if u google them u can find them out in detail 