The FIRO-B tells us a great deal about our individual desires for interacting with others. Is it possible that the results are inaccurate or someone could fake his or her responses?
Sure, someone could consciously decide to answer in a way that makes him or her appear better, particularly when used as a recruitment tool. People are often quite conscious of the desires of those giving them the test, so the results can be skewed.
However, that's less frequently the case than other causes for inaccurate results. The most common reason is major life events that lead to intense self-reflection or temporary withdrawal from others. Examples include getting divorced, getting married, getting fired, retiring, looking for a new job, graduating from college, death of a loved one, etc. Any or all of these can affect how a person views him- or herself at the time of taking the FIRO-B.
In one study using students who had recently suffered through the death of a parent, researchers found the Wanted Inclusion score to be higher than in the control group. Interestingly, men in this group also scored higher on Wanted Affection, while women scored lower than the control group. The theoretical explanation was that the men were using "overpersonal" compensation, while the women were using a form of avoidance.
Other examples include cultural differences about how needs are expressed. Some cultures don't allow men to show any emotions at all, except in extreme situations such as war or winning the World Cup. Some people might struggle with the vocabulary or language of the questions, particularly those whose first language is other than English. Some people also consciously or unconsciously avoid extreme responses, answering near the middle on all questions. Others may feel pressure from their environment to respond a certain way. The classic example is when the FIRO-B is given as part of a teambuilding training. People understand they should fit in and support the team and will answer accordingly.
The interesting part about those who try to alter their answer to fit in is that they rarely make big changes. They fear being discovered, so they make minor changes to their responses. However, because they don't know the cutoff score for each response, it's unlikely they'll change their answers enough to affect the outcome. The FIRO-B is well designed in this regard. Faking is usually successful at the extremes, i.e. "make myself look great" or "make myself look terrible."