We bought our tandem off craigslist, and I bought my Surly from ebay. I bought my roadbike from a shop in Wilmington, used. All good experiences. I've sold 2 bikes on Craigs. One was in like new condition - it was too small. The other was in very good, but used, condition. I went to a steel framed touring bike.

But - you need to know enough about bikes to know what you're looking at when you start. And you need to have an idea of what size. Sure, there are bad ones out there, but there are good ones too.

CA