Hard work man...Calling your sphere, call arounds for other listings, door knocking, open houses, networking events, social media, forums like these, etc etc. 

The condition or effective age is.   30year old property can be beat to crap. 

smells shady to me, however the the fact that he wants to put as the leasse wouldn't concern me so much since would put his name and the LLC on the lease and you would take his personal social security # to run a background check either way, but the fact that he told you that he is planing to sublease it that a red flag to me.

It wasn’t in the best condition.

From the pictures, the property looks in decent condition.

The only other thing to consider is condition. 

A mint condition Uptown duplex may be well north of 10 and a property that may not qualify for FHA (due to condition) may be 5 to 6. 

All said, there can be numerous reasons a property is listed for an extended amount of time that have nothing to do with the physical condition of the improvements.

Document condition of every unit at time of purchase.

Assuming it's your own house,  I'd look for the big ticket items and the condition-- how old is the roof/HVAC/electrical/plumbing, as those will be your most costly repairs.