Do not take this to mean any certain company is this way but can tell you two who have done this, Dell Computers and Sears.
It may be ZERO for X time but then you get hit with back interest at very high rate if you run the full period of the loan. Not being late, not missing a payment. So less say it have ZERO rate or NO PAYMENTS due for a certain period of time. Well say that interest rate is low for 36 months but they will break up the payments into 48. So you are billed for a payment on a 48 month period and do not realize what is going on. At the end of 36 months wham...since it is not totally paid for back interest now hits the loan.
Again, I know for fact Dell Computers and Sears has done this. Very dishonest to me. This is the reason some furniture chains can make hugh profits with NO Payments for say 6 months.
But there is still a cost to Zero interest, notice they are now being little more honest (car companies) with zero interest or few thousand in rebate.
Exactly how does this relate to the John Deere 0% for 36 months? What you've described is not how the John Deere offer works - and you can pay the tractor off completely at any time with no penalty. Having purchased two pieces of equipment from John Deere 0% is exactly what it is and not your scenario of:
It may be ZERO for X time but then you get hit with back interest at very high rate if you run the full period of the loan.
All you have to do is ask the dealer and read the purchase agreement - which is what you should do with any transaction - including the supposed ones from Dell or Sears - if you don't, and the terms are not to your satisfaction, as always, you have no one to blame but yourself.