1. A retail checkout system comprising: a visual sensor; a non-visual sensor comprising one of a magnetometer, a millimeter wave scanner, a spectrometer, an ultrasonic sensor, and an infrared wavelength sensing camera; a scale; a database of features of known items; a processor; and a memory coupled to the processor and comprising computer readable program code, that when executed by the processor causes the processor to perform operations to: extract at least one visual feature of a purchase item from an output of the visual sensor; extract at least one non-visual feature of the purchase item from an electronic signal output of the non-visual sensor; receive a signal indicative of a weight of the purchase item from the scale; identify a group of candidate items among the known items based on a comparison between the at least one visual feature, at least one non-visual feature, and the weight of the purchase item and the features of the known items; cause display of information identifying the candidate items; receive a command selecting one of the candidate items as matching the purchase item; and adjust information in the database that defines the features of the selected one of candidate items based on the extracted at least one visual feature and at least one non visual feature of the purchase item.