Apparently, that seems to be the common excuse everywhere, including in NYC. You can get away with it if your agency has a stellar reputation of providing consistently high-quality girls, but if your agency is known to be hit-or-miss (like the ones where I'm at), many mongers will be skeptical of paying 320 an hour to try a new girl, even if the new girl really is of high caliber. Too many mongers have been burned by paying 300 an hour for a mediocre provider. At 320 an hour, it's simply not worth the risk.