I require deposits for tours and incall(I don't keep one). On tours, a lot of guys wait to see if I make it to their city before they book and I always tell them my deposit guys get priority booking. That second trip, they pay the deposit. A deposit is easier to get than a cancellation fee. And there have been cases where ladies have traveled after receiving deposits only to have the guys dispute it later and the lady loses out.
Should be no worries if the lady is reputable and known. Because we are not going to tank years of reputation on a percentage.