Text-based media are devoid of paralanguage (short of emoticons). There are no cues to tell you the emotional intent of a speaker, such as body language.
Therefore, unless explicitly stated to the otherwise, AssumeGoodFaith. An optimistic approach will keep you out of a lot of hot water. Often, people really do have good faith intentions and wish to resolve any disputes amicably. Sometimes they are trying to make friendly jokes (a little jab never hurt anyone). Sometimes, they may even be trying to ZenSlap you.
AttitudeAdjustmentTool when correctly used. :o)