The problem with jerks is that they don't always reveal themselves until you're already working with them too closely to cut ties. To avoid getting into a sticky situation, watch how the people you meet treat strangers. Photo by Gideon.
As business site Inc. points out, jerks are often nice to the people they need something from, but they will start showing their true colours to strangers. Pushing through to the front of a line, getting short with a waiter or being aggressive in traffic. How that person interacts with strangers can tell you a lot about how they will act when you start to get in their way:
Watch reactions to strangers: Go to lunch and pay deep attention to how the wait-server is treated, or in a cafeteria, how the candidate maneuvers through a line at check out.
Of course, everyone can have a bad day, so it's fair to watch over a period of time. However, the way they treat others should be given the weight it deserves. If you can't trust your potential business partner to be courteous or fair to your waiter at a restaurant, you probably can't trust them to be fair to you later on.