Reisha,
You are not alone. I too get that response at times and my favorite is "you seem to nice to be a stepmom." Yes, someone actually said that to me.
This past summer, I was talking with a group of stepbloggers at a blogging conference and we all shared stories regarding this exact topic.
In addition to some people seeming to be put off by a stepparent, there are also seems to be some hesitation in admitting you are a stepmom. I've had countless talks with people and after sharing that I'm a stepmom and what I do, they will finally say in a whisper "I'm a stepmom too."
I think some of it comes with the false perceptions that our society has cultivated about stepmoms and a lot comes from misunderstanding.
When I get the brush off I just think of it as their loss and don't give them any more of my energy or thoughts. Remember to never take it personally and to know that the reaction has more to do with the person giving the reaction than it does with you.
Would love to hear from other smoms as to whether they've received the brush off or not.
Hope this helps. Stay Strong and Press On.
xoxo Heather