When is Owner Finance a good idea?

[Youdo Thirakul]

Just curious when is an owner finance a good idea?  And what kind of term is reasonable ? 

I know someone that has a 4plex and a duplex that want to sell it but unfortunately I don't have cash or enough finance to for what he's asking for.  Each building have tenant but one vacancy and need some work.  I'm not sure if he's free and clear the property but I'm going to check it out this saturday and maybe bring up owner finance as an object to get these properties.  I think he's tired of being and landlord and updating them.  There's no realtor involve so the price can be negotiate but i know he still want a high price.

I was thinking maybe putting down 10-20k for each property and paying him whatever the tenant rent is so I don't have to put any more money out of my pocket beside some of the repair and eventually I will own the property in couple of years. Any advice ? should the property be lower then the value of the property or that doesn't matter because of appreciation ?  I saw couple of houses on CL that offering owner finance but the listed price is high, does that make sense to buy as well?