It's definitely a good tool in the toolbox for any investor but I generally find them to not be useful. First off, many sellers don't have sufficient equity to offer seller financing. And even if they do, they have to be fairly motivated to be willing to do so (even if you've built rapport and all that good stuff).
If they are motivated, usually that means the property needs work and they almost certainly won't lend over and above what you buy the property for. So you'll need to bring your own money to do that. And they'll want you to pay off the loan pretty soon (and usually will you as the rate will probably be higher than banks) so there's that too.
For this reason, we definitely prefer private lenders as they will (if you've built trust with them) often lend on the rehab too. But of coruse, getting private lenders isn't exactly easy. So there are definitely times when owner financing makes sense.
