I don't invest in the rust belt so am not familiar with the details of the city but doing a quick and dirty check-
Looking at greatschools.org, the school districts appear to be poor to fair (2-5) and the rental vacancy rate in the city is 9.8% according to the US census, which is high. So the rental market is probably relatively soft in the neighborhoods these houses are in. This lines up with the fact that three of the properties are vacant.
Second, a portfolio of nine houses worth $323k is more difficult and more expensive to manage than a portfolio of one house worth $323k. There are nine roofs, nine HVACs, nine hot water heaters, etc. In general, it is going to cost a much greater percentage of rent is maintain those nine houses than it is going to cost to maintain that one house in a more expensive location. Is a new roof in a more expensive location going to cost 2x more than one on these homes? Maybe. Is it going to be 9x? No way.
Third, as walt pointed out, the population in this area of the country is shrinking. Chances are these houses will have no appreciation over the term of ownership. While appreciation shouldn't be relied on for property profitability, it's unwise to ignore population and job growth when choosing investment locations.
People are lazy. They want to use a rule of thumb- 1%, 2%! And they're only 30k a piece! What a deal!
Thankfully, mustashians are not. If you sit down and calculate the actual cost of ownership on these 30k houses...
Rent: $750
P&I: $136 (presumed a 4.5% portfolio loan; 1/9th share)
Taxes: $75
Insurance: $45
Management: $75
Vacancy: $247 (real time vacancy of 33.3%)
Repairs: $75
CapEx: $250
Total: -$253
CapEx from a nifty table in a biggerpockets article on 30K houses: