I think the most realistic scenario would be someone who wants to buy a $20,000 tractor and has $20,000 cash.
If you buy the $20,000 tractor for $19,000 ($20,000 minus the $1,000 'rebate'), you have $1,000 left over.
You "saved" $1,000.
-- or --
If you buy the $20,000 tractor for $20,00 (no 'rebate' because you are getting the 0% loan) on a 0% 5-year loan, you will pay $333.33 each month.
Assuming you are making 5% per year on your money (your money being the $20,000 cash you have "invested" -- bank account, stocks, bonds, whatever) and it is this $20,000 pot of money in which you will draw from to pay the monthly tractor payment, at the end of the loan you will have $2,900 left over.
You "saved" $2,900.
Going with the loan, you will make $1,900 more than if you paid cash.
Make more than 5% on your pot of money? You make more money.
Make less than 5% on your pot of money? You make less money.
If the return on your investment gets low enough, paying cash would net you more money than the loan.
The best part is, as long as you don't spend the $20,000 on somethig else, it will always be there to cover the loan... so having a loan is not a risk to you financially.
Also, the more money you spend on the tractor, the more money you "make" -- as long as you have the pot of money to earn interest on. In other words, if my scenario above was a $40,000 tractor and you had $40,000 to pay cash with or invest. I don't know if the rebates go up when the tractor value goes up. That could change things too.
Me? I envy the people that "have" the cash to buy outright. I would still finance when rates are at 0%, but I still envy you none the less. I needed a tractor NOW and financing was the only way it was going to happen. Zero % was a blessing...