All coins passing through Jambler mixers are analyzed for taint, if they're rejected for being too dirty Jambler can decide to keep them.
Jambler is not a mixer, so it's not going to take possession of the coins going through it, as you said. It's a business offering everyone a chance to become a partner or an investor in the mixing business and make some money from it. As an end user of mixing services, you have no contact with Jambler.