A sharp buyers agent will have devised strategies to short-circuit them.If you're buying, be prepared with your lending secured and be ready to write an offer on the spot if you see a property that meets your criteria. 

There was very light surface rust on the exterior of the breaker box. 

Modern code would be for there to be a dedicated 20 amp circuit with a GFCI receptacle. 

It was a deal breaker for the numbers. 

(can be held at the title company or the real estate brokerage) Then you "open title" by sending the contract to the title company (some states have realty attorneys that do some of this, I'm not sure the details for those states) When title is opened the title company doe a preliminary title report, meaning they're searching the title for all the liens and easements and restrictions, etc, and tell you what they're insuring (up to the purchase price) and what they are not.If you are doing inspections and other due diligence, appraisal, well/septic, as-built, all that gets done in the mean time, if there's a deal breaker in your due diligence period you would get your earnest money back (check with your Realtor... if you're new at this and don't have one, get a Realtor)The remaining funds for the property come when the deal closes, this would be the cash from the buyer or a lender.

Main things to look for in this price range are updated electrical wiring/breaker box.

Read my posts about lawful peaceable possession of abandoned property vs. unlawful possession of vacant and neglected property to understand why that rarely works out like planned.You remove occupants by an ejectment lawsuit filed in Circuit Court, not an eviction. 

You can also add air conditioning now or later relatively easily. if you want to add hot water baseboard the boiler pipes and time to install will cost you. if you want to do electric baseboard you might have to do service upgrade to support the additional circuits and amps they draw. 

Finding a quadplex w/financing is certainly preferred although not a deal breaker (he qualified for an FHA loan).

In terms of importance out of all that you included what would you say would be a deal-breaker/maker?