In other words, a non-citizen who cannot prove legal residency in the country can be rejected.

In virtually any situation for a US citizen you do NOT want to hold real estate in a corp such as the S Corps you have in place.

There are no restrictions and will report as normal Citizens. 

That same house was a result of a senior citizen getting scammed by an elder-abuse wanted felon who specialized in taking seniors houses (what a thing to specialize in, eh?)

When my wife and I (Canadian Citizens and Residents) purchased a few properties in the US, we held them in LLPs to avoid the double taxation problem. 

Section 5-15(a) of the Act provides:It is unlawful for any person, corporation, limited liability company, registeredlimited liability partnership, or partnership to act as a managing broker, real estatebroker . . . or to advertise or assume to act as such broker . . . without a properlyissued sponsor card or a license issued under this Act by the Department, eitherdirectly or through its authorized designee. 225 ILCS 454/5-15(a).A license issued by the IDFPR certifies that the real estate broker has fulfilled all of therequirements of licensure under the Act. 225 ILCS 454/1-10.As of December 31, 2009, the Illinois Real Estate License Act of 2000 provides for a privateright of action when private citizens can seek to stop the unlicensed practice of real estatebrokerage. 225 ILCS 454/20-21(c).Other than as provided in Section 5-20 of this Act, if any person practices as a realestate broker, real estate salesperson or leasing agent or holds himself or herself outas a licensed sponsoring broker, managing broker, real estate broker, real estatesalesperson or leasing agent under this Act without being issued a valid existinglicense by the Department, then any licensed sponsoring broker, managing broker,real estate broker, real estate salesperson, leasing agent, any interested party, or anyperson injured thereby may, in addition to the Secretary, petition for relief asprovided in subsection (a) of this Section.

Citizen owner occupants and probate.2) Google Search (AdWords) - You want to spend all can here (on a properly structured search-only AdWords account).  

I know my grandparents were victims of a scam and its a legitimate concern to senior citizens.

That really dilutes the absentee pool for us in our FL markets.Owner Occ's are fine, but you can lose you shirt mailing to them as it's harder to find the motivated sellers in that pool.So we go after particular owner occ groups -such as senior citizens who are more likely to be moving and have a home that has not been updated in a couple of decades.  

Also, Non-US citizens cant have civil judgements deemed against them on the local level, as US courts dont hold jurisdiction on foreign non-citizen individuals in foreign countries.