Frankly, was not aware there are so many arm chair "financial planners" on here.
The whole debate of "paying zero interest" is better or "cash should get a discount" is meaningless AS YOU DO NOT KNOW ALL THE VARIABLES. Zero interest in theory is better than paying cash - assuming the buyer has both options - provided the buyer has income to make the monthly payments and not effect their credit score/debt to income ratios - and there are no other viable options to the zero percent offer. All of these criteria are pretty narrow though.
Income is typically a limited amount...even if I work overtime, I am limited in the number of hours of OT I can work...and even if I demand a raise or take a higher paying job...my salary has a ceiling. Now if I'm a doctor making 300k+ a year....buying a 20k unit is probably not a problem either way - and for the 2 people on this forum who meet that criteria - good on you, job well done - stop reading here. For everyone else you need to begin by figuring can you afford the payments without effecting your budget and credit profile otherwise - if so, its going to come at a cost above "0" likely.
Then as mentioned - are there alternatives. Again, many makers offer "0" percent financing in house - and if those are the only makes you can consider - then that is an easy decision. BUT - as the original title of this thread suggest, used is an option. Perhaps there are no quality used units available local (rare - but clean used can be scarce at times in some locales) - of course used tractors exist in other markets and we have trucks that can haul these at a cost anywhere in the world - so within the lower 48 is not a problem. Its a cost to factor in - and on a unit that sells new for 11k, shipping cross country is probably not cost effective for a 1 year old low hour unit...but the higher up the food chain you go, the better the shipping cost ratio becomes.
And of course again as mentioned - many brands offer substantially similar performance/features. Of course some things will limit your choice...using the example of my friend, a union tradesman. They need a 1 ton diesel and it must be from a union company...so his choices are limited. If they could get by with a half ton gas truck- there would be many more options. PREFERENCE is a choice, not a requirement...my grandfather taught me long ago the only color that matter when dealing with equipment is green - as in $$ - and cost is not measured by cost of acquisition alone, upkeep is part of the equation too (lets put aside resale for the moment - assuming this is a long term purchase - so resale is not a great of a factor). There is no reason most people are limited to dealing with the closest dealer other than PREFERENCE.
Bottom line is - used is TYPICALLY cheaper - however there are exceptions to the rule, and PREFERENCE many times over-rides practicality and new is more popular as the cost is close enough to justify the expense for many people. New is presumed (in my opin often wrongly) to be less likely to fail than used and be lower cost of repair and payments are more easily justifiable to many people than spending accumulated savings. Again, can i invest savings at 2% in CD - sure...but that interest only applies every 90-180 days in general - and i cannot draw down the principle to make the payments. Are there 2% savings rates out there - yes, but in general promotional only in nature and require either a large account (25k+) or have a low limit (5k) and most always expire after a term of 90-365 days. So again - in theory could I invest my 25k for a year for 2% and take advantage of the savings...sure...but still have a year of payments to make (so either need to set back about 4k for payments or be prepared for the budget hit) and the interest earned will only be $500.
Im not even going to start on used trucks/autos. I've worked in the field - and if some of the people in this thread understood how these people earn a living - it would completely change the way you "negotiate". All I can say is these salespeople see anywhere from 35-200 prospects a month - and sell anywhere from 5 to 40 units - so a 10% "close" rate. They know how to close profitably - and sometimes that means letting the buyer who is demanding a unit at a bare bones profit walk. Sales numbers are nice - but higher bonuses are nicer...no bank account cares that you sold the most cars last month..they care what your draw was. Used is a different beast than new in cars (and tractors) - we all agree clean, low miles/hours used is hard to find cheap - and when I only have 1 of something and many potential buyers...I need to maximize profits. Even new - certain units I am limited in what I could acquire - so acting like you are the only buyer I have interested is likely to turn off your salesperson quickly. The know they can close much better than 10% - but opt to service only the profitable clients - no point making a nickel on 20 customers when I can make a dollar on one sucker and deal with 5% of the customer demands (free add in's, service specials, ect - keep in mind sales gets little to zero break on pricing...even in the same dealership - while the profit goes to the same company - 2 different departments/cost centers and making service/parts money is a low priority for sales).