A walkthrough is when you show your prototype to a stakeholder and you want to make sure they see and note absolutely everything that might be a concern. The purpose is to give the stakeholder every opportunity to spot a problem. The product manager usually drives, but if the stakeholder would like to play with the prototype we are happy to let them. You are not trying to sell them anything, you're not trying to test on them, and you're definitely not trying to hide anything from them.
