If your finances are like many Americans’ right now, you may be feeling tempted to sign a room lease on that extra bedroom in your home. The extra $700 each month would certainly be useful, and sometimes you can grow to be close friends with your roommates. But how do you know if they’re going to prove to be clean, reliable, and pleasant to live with? Here are some of the worst offenders in the roommate world, and how you can spot them before signing a room lease with them.

Bad Roommate 1: The Bum
We all have friends like this, people who never have any money, and when they do, it’s a dollar short and a day late. They ask you to pick up the bar tab, they ask you for cigarettes, they ask if you could grab the bill at the restaurant because “they don’t get paid until next week.” You don’t want this person as a roommate: they will not pay their rent on time, which puts you in a position where you can either keep nagging them until you receive it, or filing for eviction on the person you live with. Not a pretty picture.

The way to spot these people is threefold: first, run a credit check on them. Second, confirm their employment (and history – how long have they had the job, and the job before that?), and third, confirm their income. Their income will tell you if they can pay, the credit check will tell you if they will pay.

Bad Roommate 2: The Slob
Hey, we all leave the occasional T-shirt on the floor in the bedroom, but some people are just plain filthy individuals.

They leave bowls of half-eaten ramen noodles sitting on their bedside table for weeks on end, they leave piles of dirty pots and pans on the stove, and worst of all, an insect colony has taken up residence in their bedroom.

The most reliable way to spot the slob is simply to show up unexpectedly at their current home, with some sort of good reason, such as dropping off a rental application or a preview version of the room lease. If they don’t invite you in, ask if you can use their bathroom, and get a good look at the way they live. A few clothes on the floor or half-packed boxes lying around is all right, but chaos and old food lying everywhere is not.

Bad Roommate 3: The Hostess with the Mostest
It’s nice to be able to invite people over for a glass of wine or a dinner sometimes, but some people’s friends are always hanging around the house, shotgunning beers and chucking them on the floor, or cranking bass-thumping music at all hours of the night. Unfortunately, these people are the hardest to spot before living with them, as their gregarious behavior won’t show up on their credit check or employment record.

The best way to spot these people is to ask oblique questions like “What do you like to do for fun?” and “Where do you like to hang out?” Listen for them to list off activities that consistently involve a lot of people, and for bars frequented by savages and Philistines, and simply go with your gut; you’ll pick up on their cues subconsciously.

Signing a room lease on your extra bedroom can be a great way to bring in some extra cash, but it can also cost you much more in money, time, and lost sleep. Screen your roommate applications carefully, and only sign a room lease after running a credit check and doing every other piece of homework you can about a rental applicant.