The owner is willing to sell a duplex.

I have attached the recent improvements to it.

You should be able to get a regular loan on this.

It is fully functional with no repairs needed(as far as I know anyway.) 

$40k.

It has a tenant in one unit. She has been there 3 years. The bigger unit moved out last month, but he is willing to get you a new tenant. He says it only takes about a week there. Or, he can put in the daughter of the current tenant with her family at a reduced rate and they will probably be there for years.

The bigger unit pays the water bill, so the rent is $650 instead of the $700.00 he used to charge. 4bed 3 bath

He is willing to owner finance with $10k down. Simple interest @8% loan 30K 677 monthly payments 3 years. 

Has anyone heard of this kind of loan? And what are your thoughts? This properly will be my first rental!

10k is over 20%. 

20% is normally what is required to get a normal loan and you would get a lower interest rate over a longer term which means lower monthly required payments, although you likely would pay more its nice to not be required. 

I personally haven't done seller financing and have been a bit skeptical just due to allot of shady people out there who attempt it. 

is this an actual duplex or a single family home that somebody divided up? maybe post a pic of the front of the place