No offence intended here but this has now gone totally off-topic. Discussing whether or not the comments are rude or not has no relevance on the original topic.
Yes, he posted information on how to spot fake screenshots on e-bay, amazon, etc., however, if you're not doing real world trading, you don't have to worry about it.
There is no further point to this topic other than to say, don't break JAGeX rules and you have nothing to worry about.