Two days ago I caught a carpenter bee (Xylocopa sp.) engaging in nectar robbing. I do have a few words to say in favor of the defendant.
One of the photos shows the carpenter bee about to head through the front door of a Hooker's Evening Primrose flower. The other photo shows the same bee cutting a hole in the side of a different flower, a few moments later, in order to remove nectar. But notice that the bee is partly encrusted with pollen.
In other words, one flower was open enough that a front-door entry (and acquiring/dropping off pollen) was possible. When the other flower wasn't open enough to allow that level of honesty, the bee resorted to breaking and entering. So the bee was being as honest a pollinator as circumstances allowed.
For other images of carpenter bees, please visit this page.