As a data point, Customs does inspect if you have large tax-free purchases. We made a couple of 4-figure USD purchases on previous trips and did not trigger any inspection. On a recent trip in November, we made a couple 5-figure USD purchases and when we were checking in for our flight, the JAL check-in agent at NRT noted that we were flagged by Customs for inspection and they could not check us in until the Customs agent came to the desk. The Customs agent came with a print out of everything we had bought and highlighted the high-value items and wanted to see them before allowing the JAL agent to check us in.