Am I getting a good deal-How to renegotiate.

I purchased a loft in December 2012. I put down a deposit equal to 20% of the purchase price. The seller is holding the note. The note is supposed to start this December at a rate of 6% per year. It is a mortgage amortized over 15 years with a balloon payment after 10. Under the terms of the agreement, the seller has been allowed to continue living in the loft only paying the real estate taxes and... [more]

I purchased a loft in December 2012. I put down a deposit equal to 20% of the purchase price. The seller is holding the note. The note is supposed to start this December at a rate of 6% per year. It is a mortgage amortized over 15 years with a balloon payment after 10. Under the terms of the agreement, the seller has been allowed to continue living in the loft only paying the real estate taxes and maintenance. The plus side of this for me was that I would not be accountable to pay the note until the seller moved out in December 2014. At this point, the seller is interested in staying longer and I am deciding what I should do. I don't know if I even got a good deal to start with. I know that the interest rate was not good--6%. Any ideas what you would do in this situation and what I should negotiate with the seller if he would like to stay past December? Thank you. [less]