No, buying a decent used bike at a bike shop makes sense, buying a wally-world junkster doesn't. If your local bike shop doesn't sell used bikes, then find a shop that does.

Last year, a friend of mine was looking for a bike, in the $200 price range. I went to the local bike shop, and found 3-4 bikes in his price range, all in good shape, but noooooo, he went and bought a piece-of-schwinn from ***-mart. The chain kept coming off. The wheel wasn't trued. The BB started making grinding noises. All this within 3 months. He asked me to fix it. I told him to take it back for a refund. He threw it into the dumpster last week, exactly 14 months after buying it.

Good deal? Hardly.