Speaking as someone who has played in the lifestyle for over 10 years as well as being a professional, I've experienced a lot of what you're talking about. Being a dominant woman does not mean that i want to dominate every Tom,Dick, and Harry that crosses my path. Some men have submissive urges that I have no interested in. Others, like my current play partner (who isn't a full-time slave, but who I play with very frequently), has very similar interests as me; dominating him gets me wet and charges me with intense energy. He and I have also known each other for almost three years. We are friends, lovers (to an extent), and trust each other indefinitely. That trust is what sets him apart, I think.
Some professionally dominant women are into all aspects of domination, and it doesn't matter who it is or what they want. This is really rarely the case, and most dominant women will question you thoroughly before agreeing to a session. Real life BDSM relationships work in this manner too. Lots of discussion, communication, and talk of hard limits, boundaries, and must-haves is really important.
Along the lines of professionalism, I don't offer slave-hood outright to just any client. If i had a client and the chemistry was simply amazing, it's something I'd offer, not something he would ask for. He should know better.
Now, as for convincing a lady who isn't dominant by nature to dominate you? That's tough. Some women do have dominant fantasies and leanings, but social constructs constantly tell women that they aren't supposed to be dominant. Lots of communication can help, but you really have to have patience and a willingness to be open-minded and expectation-free.
Hopefully that made sense.