I don't think it's common practice for the person who assumes the lease to make good on the down payment for the original lease holder. That's the benefit of taking over the lease, you don't have to deal with that stuff. The original lease holder should pay the lease assumption fee too.

NY is going to whack you for the sales tax on the remaining monthly payments.

Did you ask if the original lease holder paid the sales tax up front or if he put it in the lease? If he rolled it in, you're paying the sales tax twice and making good on his down payment. I wouldn't do it if I were you.

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