My wife is looking for a entry level road bike that she can ride on the weekends. I am looking at a very lightly used Trek 1.2 WSD for my wife. It looks to be in great shape, no scratches or dings, and no upgrades. The guy wants $500 for the bike. Is this a good price for this particular bike?

I think thats a fair deal as long as it is lightly used. Trek bikes seem to hold their value well over the years, I bought a 2 year old trek 1000 from a pawn shop and was able to sell it for near store value (after doing full tune up and replacing a few parts I had laying around) and doubled my money, because how well they hold value. You might be able to negotiate a lower price if it needs to be tuned up or needs tires or brake pads.