If the contract is signed I don't see that you are obligated to pay it. But, how will that effect the business relationship and the speed of the service/maintenance, etc. for the copier?

I would compromise... go back to him and tell him that you understand mistakes happen and certainly want to be fair, but the contract is signed with the PTO having signed it in good faith based on the information provided, and that you are more then willing to split the tax cost with the company out of fairness. Or at least give you a $1,000 credit towards maintenance or supplies.

I don't know the size of your school but $1,000 for us is a large sum and would impact some other area of the budget.

Our PTO purchased a copy machine for our school. We voted on it at our last meeting, and I signed the contract and paid for it. It was delivered about 3 weeks ago. When I got the price, I specifically asked the rep if it included tax, delivery, and maintenance. I was told yes to the first 2, and maintenance is separate, but the school agreed to pay for it.
Now, almost a month later, the rep called and told me he is new here from another state and didn't realize schools are not exempt from Sales tax in AZ, therefore did not charge it to us. He said we owe almost another $1000.
Our board is divided over whether or not to pay this. On one hand, had we been charged it in the beginning, we certainly would have paid, and if we don't it will most likely come out of the reps commission. On the other hand, we have already signed the contract, paid, and have the machine. Any advice?????????