@ Jasmin - I guess it depends on if you are relating this to a commercial aspect, or one of a more personal nature. If you are "posing" for a fantasy, it's not at all impossible to put on a mask and become someone else. Actors do it all the time, and many of them can be quite convincing at becomiing someone else. But it's also an act.
If its something more long term, then yes, I think most people would have a very hard time maintaining the false facade of dominance if that is not what they truly are.
Then again, there are many, many posers out there who have no clue and are predators (male and female) who are looking for an easy score or use the lifestyle as an excuse to hurt and steal. But that's always been an issue that the lifestyle has faced (plus at times we do a very poor job of policing and ejecting the predators). That's why it's always great to get reccomendations from others (gee, kinda like the hobby!)
And you are very correct in stating that to do this well, it involves a LOT more than going to your local Hot Topic to pick out a domme outfit, then a trip to the local bookstore to pick up some velcro cuffs for your "serious bondage" rendezvous at the local motel 6 with a client.
@MsElena - The GOOD dommes out there do what you are suggesting - investing the time in gaining skills, equipment and practicing till they know what they can do (the BEST do all that PLUS they do it sanely and safely). I know more than one professional bondage model who has suffered injuries (some permanently) from bondage riggers who said they knew what they were doing but put knots in the wrong places or for too long and caused nerve damage. If you don't want to do that to a client you need to learn how to do it well and safely.
Plus, its just lots more fun for both parties if you can play without risk. Sooo much more fun stuff to do...