I'm wondering the same thing because I want to ask for it. I have no experience but from my understanding, these would be my guesses:
1) No longer responsible for the maintenance or management of the property
2) no more dealing with tenants
3) guaranteed positive income (assuming all payments are made) and steady return on money.
4) loan is secured by the property that they already know the value of
5) lessened or deferred tax implications on capital gains by spreading the sale out over time.
6) chunk of change up front (down payment)
7) balloon payment after designated note term for the remainder (assuming this is how it was negotiated) wherein they can take back the property if you can't pay. Otherwise they'll just continue to collect cash every month.
The negatives though:
1) they need to own the property outright. I assume this. If not, some one please explain how it could be done short of "subject-to".
2) they don't get all the cash up front
3) they have to deal with foreclosure if you default.
4) they have to trust you to make payments
5) assuming they're selling a rental, their income from that property will eventually stop.
I hope more people chime in. Very curious how to approach someone and ask for seller financing. Maybe it's as simple as just throwing the thought out there knowing you ma my be told to F off...