What are "normal" terms for seller financing?

[Travis Bill]

Just recently started researching getting into rei. There is a duplex near me in an excellent location that has dropped in price like 35% in the last 4 months after slow drops for a year. Looks like the seller is getting desperate. Gross rents of 1000 and if the price drops again next month it'll be down to around 46k. Im thinking of possibly offering around 41-43 after the next drop but would probably need seller financing right now. What is a normal down payment and interest rates in a situation like this? Or are there just too many variables to know without asking the seller?

Any advice would be appreciated.