Ultimately I guess it is up to the forum admins and the overall policy of the forum.
For the most part I think they delete comments containing links because they are simply sick of getting spammed to death and don't want to encourage it any more than it already happens.
They will be even more skeptical when you are a new person. It takes at least a little while to earn someone's trust. You might be the most trustworthy and most authoritative person in the world. But, it is going to take a while for them to get used to seeing your high quality comments before they come to realize you are looking out for everyone's best interests.
So, my advice is to make sure that you are taking your time when answering other people's questions. Make sure you are making a real effort to help that other person. Be thorough in your explanations. Once you have a little trust equity built up, then admins will be less trigger happy when reviewing your comments that contain links.