Making offers on seller carry back

[Andrew Farmer]

So far all of my deals have been low all-cash offers. I want to start making Sub 2 and seller finance offers. When you make offers for seller carry back, what can you offer to pay them monthly? I've talked to people who offer 1/2 of whatever rental comps are going for. Example, there is a house with minimal needed repairs and rents in the neighborhood are $1200/mo. Would you be able to offer $600/mo. (principle & interest) until the balance is paid off?

I know every situation will be different but is there any rule of thumb for seller carry back offers?