Property Acquisition - Zoning Violation Issues

[Scott F.]

Looking to acquire what I thought was a triplex a couple blocks from my house.  Turns out it is zoned single family and may not be operating "legally"(which is not surprising because the entire neighberhood is single family).  Projected rent would probably go down by a third making it a horrid acquisition if the county enforced this.  Listing price recently dropped from 900k to 800k I'm thinking directly related to this issue.  

Love to hear peoples thoughts on the subjects for how they have dealt with properties like this.