I'm not so sure you can get Merriweather tix at 9:30 club box office, because Merriweather tix are still sold through Ticketmaster, whereas the other IMP shows are Tickets.com.
I'd pose the question in the FAQ section....
Yeah, Pollard, Seth was talking about day of the show at M. Post. I guess they used to charge a fee even day of show at the box office, but they're not doing that anymore.