I have the buyer ride around in a large safe parking lot. I check/adjust fit. I ask the buyer to brake. I instruct about braking. Then to shifting...I make certain that they go through all of the gears. Most buyers will ask questions. Some don't. I try ti be as helpful as I can. Often the discussion goes toward spouse, girlfriend riding issues. I volunteer what wisdom I have there. I also recommend specific things when asked, such as where to ride, an LBS I trust, or an accessory.