This is not a trick per se. If you think this is a trick and bank isn't aware of it, you are mistaken. Even if one cancels the EMI, it doesn't make any difference to the bank, in fact bank would prefer the cancellation since they get the whole lumpsum amount in one go and hence the banks can generate more early returns from that money.
On the other hand, if we had opted and continued with the no-cost emi month-by-month basis and not cancelling the EMI, you could have generated higher returns by investing that lump amount instead of cancellation. Assuming you generate 10% returns, that is approx. the same amount which you could have saved by cancelling the emi and availing interest discount. It's a win-win situation at the end of the day.