If I don't know an area the first thing I check is the online sex offender list which publishes the names and addresses of offenders in the zip code I am looking at.

Sex. 

Just found out seller is on sex offender registry too so this feels really weird to me.

There is nothing that is relevant in all circumstances and economies...Businesses related to things as basic as food, energy and sex have (and will continue to) undergo radical changes. 

People can do it for various reasons (your age, your sex to begin with).

Even if you decide to let them get added to the lease, be sure to screen.Adding a sex offender or psycho killer to your lease might upset the neighbors...

The FHA, to date, includes seven protected classes: race, color, religion, national origin, sex, disability, and familial status.

I will request a refund from Nick but I doubt he will send that to me as I am not sure if he is more obsessed with money or sex but is a truly greedy, unethical person indeed. 

@Bao Huynh How did that project turn out for you?

Below are the tenant screening that we use:- check credit; credit has to be at least 600 specially if you want the tenant/buyer to cash you out in 12 months; also there should be no 90-day lates in the past 12 months- check criminal history: no felony in past 5 years; tenant can't be a registered sex offender- check income/ verify employment; salary has to be 3 times the rent- check civil cases: no evictions in the past 5 years; no BIG civil suits judgmentsIf you're a newbie, you can't afford to get a bad tenant.