Silicon n+-in-p microstrip sensors have been developed for the ATLAS Inner Tracker (ITk). This is part of the phase-II upgrade programme for the High Luminosity Large Hadron Collider which will see a sevenfold increase in peak instantaneous luminosity. Prototype and preproduction generations of strip sensors are designed by the ITk Strip Sensor Collaboration and produced by Hamamatsu Photonics. The sensors undergo a variety of electrical and mechanical tests for Quality Control (QC) which are essential to verify compliance with specifications, monitor processing consistency, and predict the overall performance of the ITk. QC procedures are detailed and results from prototype sensors are given. A selection of results beyond the scope of QC are also presented. Topics include the effects of proton radiation, anomalous loss of strip isolation, and bias dependent changes in surface oxide charges. These studies are aimed at informing predictions of long term sensor performance.