I usually only reply to a report when I’ve chosen not to take action on a report, and the same poster reports the same post again (or PMs me). Then I’ll send an email explaining why I didn’t take action before.
As has been said, you can usually assume that the report has gone through, and that if no action was taken we decided none was warranted. (In GQ, it usually means that all of the mods have seen the report and all of us decided to take no action.)