Everyone on here has very valid and understandable points.
I think if you are starting to get your RE education, reading books, and watching video's on here and they tell you to make offers!! So you do your very basic newbie research, run the numbers, you find that investor friendly number that works. Your ready to take ACTION and make an OFFER! Then you go to the realtor and they are the ones telling you NO. That really isn't a action taking NO. It is a educated opinion based on what could be years of experience of what could happen majority of the time of why you shouldn't make an offer because it more then likely going to be NO. Talk about taking taking the wind out of those action taking sails! You didn't even get to the decision maker.
I have experienced this and it sucks.
I know there are human factors involved as far as saving reputation and not wasting time but but speaking from the buyers side, it can be deflating trying to get through a realtor so you can make true action steps.
I did like the advice to go directly to the sellers agent and at least make a verbal offer and start a conversation. Not sure if this is good or bad advice but it is a action step that could get you to a Yes.