Favorable terms when buying a Seller Financed home as rental

[Adam Smith]

I'm about to purchase my second rental using traditional means (20% down, bank, blah), but want to acquire my third property faster this time around. A very successful investor I met suggested going to my local REI meeting and telling everyone I'm looking to buy a seller financed home.

He stated that even if I paid full market value, as long as it cash flowed, it was worth it, since the return on zero down is infinite.

If you were looking to purchase a buy-and-hold rental in this manner, what sort of terms would you look for that would be fair to both parties involved? Using their rent roll, amusing it was a rental, how would you know the max price you would pay?

1) Purchase Price
2) Interest Rate
3) Down Payment
4) Amortization/Balloon Payment
5) Pre-Payment Penalty
6) Other??

Thanks!