Sometimes implying or hinting is better than explicit. Also, willingness to be a victim is a big turn on.

Expand on what the police woman said. Have a tent in the background called the raping grotto (or something). Don't show us what happens in there, but show us a queue or girls, and some women too, waiting to enter. Have speech bubbles where they describe what they hope for:
-I hope they slit my throat, rape it, and throw me in a ditch.
-I hope they cut my hands off and punch me in the face repeatedly, before gang raping
me.

Also, a hot dog stand would be excellent. A line of men and boys waiting for the girls to cut off their cocks, cook them on the BBQ and then serve them back to them (or others) in a bun. Make the boys eager and willing. Add a couple of adult men (gym teacher, visiting German TA, etc.)

For the slave market, how about someone buys a slave just to take her to the parking lot, have her syphon gas out of a car, and self immolate with it.