I live between Avon and Plainfield, I just saw a rental in the neighborhood next to me advertised for $3000 for LTR,  totally shocked - the one two doors down from me is renting for $2400. 

They had an ad online for prospective tenants advertising 200+ vacant rentals.

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Purchasing from overseas, I made my offer based on the advertised info and, believe it or not, did not uncover that 2 of the units were just 1b/ 1ba until after due diligence. 

2) How would I start to advertise, find comparable rents (I found one just up the street renting for $3500/mo)?

Once someone applies, stick to your criteria and update it the next time around.If you don't want bankruptcy, make it a pass/fail on your screening process before you advertise the next vacancy.

One of my buildings is a 4-plex, and they were somehow confused with the number of units and were only advertising for 3 of them. 9 months after buying the building only 2 units are rented out.I'm interested in hearing others feedback about the Quad Cities market.

In the mean time start advertising the property. 

Have the floors refinished and advertise for no pets. 

Also, local real estate agencies sometimes have rental listings not advertised online.