Seller financing - interest rate???

[Tim Haag]

My mom is handling her mother's estate which includes a lot with an old trailer in Cle Elum, Washington. She has an offer on the property but the buyer wants the estate to carry the contract. We are going to give the buyer a 5 year contract with a balloon payment to give him time to finance it with a bank. The sales price is $42,000 with a down payment of $9000. What is a typical interest rate to charge for something like this? Would you recommend interest only or a normal amortization? Thank you.