There are a few things that need to be known before it can be determined if the dealer is correct in his thinking. If the dealer is located in Massachusetts, I believe that the trade is deducted from the price of the new tractor. If the dealer is located outside of Massachusetts, and isn't registered with the State of MA for collecting sales tax, then the entire sale amount before the trade is taxable. If the dealer is registered with the State of MA to collect MA sales tax, then the net price is the taxed amount. I am assuming that the rules for tractors are the same as the rules for automobiles. I have searched the MA Department of Revenue website, but couldn't come up with any instructions concerning this. I do know that on the MA Sales Tax reporting form, line 2 is for "Sales for Resale/ Exempt Sales or Other Adjustments". I believe that this is where he would insert the amount of the trade when he reports sales taxes to the State. If you want a definitive answer, you can call the Massachusetts Department of Revenue, Taxpayer Service at 1-617-887-MDOR or Toll-Free in MA 1-800-392-6089.
Now, if you really want to save big on the purchase, you can take advantage of the upcoming MA Sales Tax Holiday August 13 & 14. This will allow you to purchase any item up to $2500 for personal use and not pay any tax on that item. If you purchase the loader and it cost under $2500, then there will be no tax. If you purchase the Mid Mount Mower, which sells for under $2500, there is no tax on that item either. There is no deduction for items that sell for over $2500 in this Holiday regulation. The other wrinkle is that it must be paid for during the Holiday exemption period. If you are financing the item the sales contract and financing must also be done on this Holiday. The rules for this Holiday are quite stringent and the dealer might not want to do separate sales for the loader and mid mount mower, but if it is done properly, you will have no problems. I suggest that you speak with the dealer of choice beforehand to make all the arrangements. You might not save on everything, but it will at least help you on some of the purchase. Junk...