The precept of killing is a great baseline. Very clear: if you kill something with intention, you break the precept. The factors I can remember in the kammic disecction of the matter are: the kammic weight of the one being killed, the intention of killing (and any coupling intents), the actual action, whether or not it succeeds, if, any, regret after the action, and maybe a few more factors. Giving each a realistic weight depending on the full situation will give you an average estimate of how bad it is.
The thing is that the actual action is very clear with killing no matter how obscure the situation. With precepts like stealing, lying, or practices like wrong speech there isn't really a meter to hold yourself to. I've asked around on reddit and even here before but I haven't had a proper, well-developed answer to this.
Some answers, particularly for right speech focus on following the heart or judging based on emotions, but that is the opposite of a discerning judgment and many of us follow our subtle judgement to worse kamma, not better.
A meter of 'that which is not freely given' is pretty good but refuted by the sutta that speaks of 'stealing' a flower's smell.
Other answers focus on a middle-ground, but these do not address the right course of action in situations where property becomes non-physical, or ownership of property splits, or other complex situations not faced during the Buddha's time.
At the end of the day, there is definitely a right answer to this question, and it's important to know it for this high-speed age. You need to know this before you find yourself in such a situation because the decision has to be made on the spot. The answer exists because to a Buddha's range, there is an absolute understanding of whether an appropriation of property is stealing or not. This absolute knowledge, assuming it is not the result of direct kammic vision, can be practiced by normal people too.
Edit: For a precept like stealing, ownership is arbitrary and can't be properly defined. Abusive speech is arbitrary and again changes from person to person. What might be a violation of right speech to one person isn't to another. Lying is pretty objective, but also has its' issues in getting proper communication across. In right speech, abusive speech is subjective: some consider certain words abusive, so if you speak to them in such a manner it won't be right speech. Others might not, and then there should be no violation of right speech in that situation even though everything you do is the same. So how do you find that line of practice where you can say, "I am properly keeping this or that precept, without worrying about self corruption?"