What if he's a registered sex offended?

But it's not protected under the Federal Fair Housing Act.Here's a link to what's protected under the Federal Fair Housing Act:RaceColorNational OriginReligionSexFamilial StatusDisability   Even apartments.com's own Terms of Service don't seem to prohibit what you posted (again, as long as you didn't reference source of income):Compliance with Fair Housing LawsAll Content is subject to federal fair housing laws, which make it illegal to indicate in any advertisement any preference, limitation, or discrimination because of race, color, religion, sex, physical or mental disability, and/or familial status.

That was until the Persians came, and a man who was often derisively called "the whoremaster of Athens," aided by the contributions of, yes, despised, belittled, and often-abused sex workers, essentially saved the core Greek institutions of western civilization at their inception, in the naval battle of Salamis, circa 480 BC.

These days, state laws hold landlord responsible for renting to sex offenders and criminals, and I'm not sure how my insurance company would handle it if one of your subtenants, a known child molester, molested a neighbor's kid.

@Andrew PappasDon’t forget to do a sex offender search too. https://www.mshp.dps.missouri.gov/CJ38/AreaSearch

In our market we have one city that gives the voucher holder her/his own bedroom and separates the sexes for anyone over the age of 10 into two people per bedroom.  

There are 7 protected classes at the federal level.Race, color, disability, religion, sex, familial status and national origin.Here in MA, we have 15.  

Be sure to google the property address, I have come across sex offender tenants and news of big-time police drug raids by doing that.

That is a look that appeals to both sexes.

Also if this group is looking for a more detailed response  in addition to my adverse action notice as to why we are choosing another group, are the reasons listed above okay to use since they don't fall under any discrimination laws ( age, sex, religion) Thanks for your time and help with this