Sociopaths are literally incapable of feeling empathy. Nearly everything else flows from that inability. However, it must be remembered that most sociopaths are not violent. They seek to satisfy their internal desires and if those can be satisfied legally, they will do so. The point where they become dangerous is either when those desires can only be satisfied illegally (usually, but not always, sexual sadism) or when they achieve power. Because they tend to be so single-minded and lack empathy, the ones whose desires are legal will quite often end up in politics or the high levels of business as both environments select for those who can do terrible things without remorse. Another thing an assessor would be looking for is animal abuse. Sociopaths think nothing of abusing those weaker than them and that's often revealed in their actions with animals, either through outright abuse or neglect because there is no capacity for empathy, no ability to place themselves in another's place. So they simply don't feel remorse, guilt, sympathy or conscience (or fear but we don't yet know why).
That said, it's not unusual for a fairly normal person to satisfy one or two criteria on Dr. Hare's list. I satisfy one of them myself. The difference is that the sociopath will satisfy all but one or two.