Hi Felipe,where are your properties located? 

If you're lucky enough to get a free and clear property where the seller is willing to finance, this reduces much of the risk associated with seller-finance.I would make sure the title is then moved over to your name, especially since there is not a risk of a due-on-sale clause being triggered.

There will be fluctuations on rents and much of it is property and timing dependent and not necessarily market dependent. 

Also make sure you are comfortable with some holding costs if the units don't get rented right away (if vacant).Also look into if there is rent control in the area that the property is located.

Look for properties with value-add potential, plan renovations carefully, and use tools like the BiggerPockets Rental Property Calculator to analyze deals.

I'd keep an eye on ancillary properties that become available. 

Quote from @Chris Wagner: Hello everyone,I have a property that had sewer damage that costs me $3300. 

It is hard to really keep up with those kinds of trends unless I budget 10k a year in updating the property which I am not going to do.I participate in our local council/mayor meetings.

Because the property tax as a non-owner occupied property is about 3-4 times the amount of a owner occupied property.  

She knows he probably owns at least half the property too right?