What am I missing here..?

[Jacob Wright]

So I'm very very green to investing and real estate in general. However, I am very handy and eager to learn. I am basically interested in house hacking with a duplex at first and then moving onto more multi family buildings in my college town. I have been looking for duplexes to kind of check out the market and see what's out there but I feel that I am missing something. I have found a duplex on Craigslist. Built in 2002. Each side rents for $700/month with one side currently inhabited. Asking price of 159,000 but has been on the market since December. This is all hypothetical but.. If I made an offer of 130,000 and it was accepted I have an uncle that would be my money for 20% over 30 years. 130,000 * 20% = 156,000 aka $433/month payment. So what I am seeing is that my tenant would pay my mortgage and I would make a little extra cash. What am I missing? It can't possibly be that straight forward lol Thank you in advance for all the help