Have you looked at the FAQ as the EXUP is not the only thing you should be looking at?The first thing you should do is ask the owner where the EXUP valve is, if they don't know then walk away as they should be servicing it once a year. If they can point to the cover then ask them to remove it (2 minute job), if they can't because the bolts are seized, walk away. With the cover off make sure both cables are attached to the pulley and ask the owner to turn on the ignition, you should see the valve reset to its default position, if it does then all is good. If the owner fobs you off about making these checks then walk away.