No, there are only 2 plugs per cylinder, the SA obviously doesn't know what he's talking about. Dealer charges about $12 per plug plus labor (2 hours or so). I think seizing is mainly the boot that goes onto the plug, the plugs are really easy to come off after I took the boots out. I replaced them after 6 years (53k miles) of ownership and they are dirty/corroded somewhat. If you are going to keep yours for a while, it doesn't hurt to replace them and replace them on your own to save some $$$.