How often do you think people (especially with Global Entry) get caught with undeclared items (i.e. carrying >$800 in bought goods or carrying food, but marked 'No' on the kiosk)?
Went through GE kiosk recently and answered 100% honestly (had well over $800 in shopping purchases, and some food) and the CBP officer thanked me for my honesty and charged me a very low tax rate rather than the 'true' rate. He said a lot of people with Global Entry don't do this properly and get caught.
This would be entirely accurate. Not declaring items, GE or not, is going to get you the "correct" rate. Declare that stuff, be kind, you'll get a lower rate, sometimes.