Yeah this is normally the reaction I get. I guess there is informal roster system going for walk-ins and they firstly try and get you to take the next girl on the roster. When you say you want to see if there is anyone else they pretend no-one is available hoping (probably correctly) that you are unlikely to back away now seeing as you have made the effort to come in.
I have walked away a few times but only if I get a sense that I am not going to click with the ML or she gives off a bad attitude vibe.