Products aren't going to get pulled immediately if someone complains. DriveThruRPG will have users flag titles that they look over. You get a product with 100+ flags, likely that's a hot title that needs to be internally reviewed asap. One to five flags? Much less so and can be put on the back burner a bit.
And very quietly they can put restrictions on the users that report stuff. They might ignore accounts less than a month old, or accounts that never made a purchase to weed out people spamming flagged content for a product they have a beef against. Even better, if a user is constantly flagging content they feel is okay for adults, DriveThruRPG can quietly move that user account into the trash column for reporting questionable books, and effectively just ignore them.
Best of all, users will never see this. All they know is that they reported a title and get an automated email confirming the report was received. The decision to pull material is all in DriveThruRPG's hands.