There's no complaint about the property online reasearch.

But her boyfriend has no Social Security Number to check his criminal record.

Make sure to include credit score, income requirements, prior evictions, and criminal history. 

(When we get complaints from apartment A that apartment B is noisy at 1 am, especially if there is yelling and possible abuse or criminal activity, we instruct them to contact the police and keep a record of the time, date and description of offensive activity.)What we do in situations like this:  interview the other roommates (separately) to try to get a focus on the entire picture, and don't simply assume the 'victim' (or perpetrators) is being entirely truthful and accurate (nor should you dismiss their complaints)--you need facts. 

Screening tenants- use a background checking service to screen for criminal & eviction activity. 

—In all criminal cases, contempt cases, and other cases filed pursuant to this chapter, if a party has sold, leased, or let real estate, the title to which was not in the party when it was offered for sale, lease, or letting, or such party has maintained an office bearing signs that real estate is for sale, lease, or rental thereat, or has advertised real estate for sale, lease, or rental, generally, or describing property, the title to which was not in such party at the time, it shall be a presumption that such party was acting or attempting to act as a real estate broker, and the burden of proof shall be upon him or her to show that he or she was not acting or attempting to act as a broker or sales associate.

The higher the risk, the more steps you take to mitigate that risk.I use a score sheet and award points based on various objective factors that represent risk: credit score, collections, judgments, evictions, criminal record, rent-to-income ratio, length of tenancy at last rental, number of late payments, length in current job/career, and so on. 

You can offer a discounted application fee for this situation as you're really only wanting to run criminal screening and therefore won't need to spend time going through references.While it's great that they're asking, I'd expect that the most likely outcome is that they have him stay, the brother stays however long, then leaves.

Questions for any eviction agent or attorney:  1) If I go with you now, when do you file the complaint? 

Caveat - This is different if you work with a company that gives some kind of guarantee of tenancy or ROI - but the term "Turnkey" is tossed around somewhat loosey-goosey here on BP and pretty much everywhere else.Some common complaints about a turnkey purchase are junky rehabs, bad tenants, early vacancies - however those really aren't turnkey problems.