When I think of Mistress the first thought that comes to mind is trampling.  I guess that is why I've always skipped those ads

Personally, I use this title as a way of hinting to submissives that I have another side of me ... other girls may simply use the term because it sounds cool and implies that they are your secret affair.  One thing is for sure, any girl (or "Mistress") in the BDSM arena knows not to spring THOSE particular experiences on a man without first having discussed it at length to avoid any liabilities.  The easiest thing for you to do would be to just ask and communicate your concerns, preferences, etc.