HELP! How find qualified tenants in a rough neighborhood

[Grace Wang]

I recently purchased a 4 plex in a rougher neighborhood. Many people responded to my vacancy units ad on craigslist. 

However I am running into problems that neither they are not qualified, or qualified tenants don't like the neighborhood. 

The criteria I used: 1. no criminal/eviction history. 2 good rental/credit history. 3. Make 3 x of the rent household income ($2500 minimum). 4. able to pay first and last month of rent along with $300 security deposit. 

The ad has been posted over a month now, I  start to wonder what is not working: 

1.  I can lower the rent, but it might attract wrong types of renters.

2. I can lower the income requirement?  

3. I need to look into section 8 tenants? 

Any advice would be very appreciated. Where do I find more information of requirement of section 8? what paper work would be required?

Thank you everyone in advance. 

Grace