Weight Cheapie (Chinese crabon fun)

I'm wary of second hand frames due to the propensity of bike theft, and, well, people sell bikes for a reason (i.e. they're fucked) and carbon one's are tougher (IMO) to spot the dudds.

Just on these two points;

1) people change frames for soooo many reasons. From looking at this and other forums it's because they either, want an "upgrade", or because they don't use it and want the money to buy something else.

2) Yes you can look for the angel of forks, bulges around the tops of tubes, etc. but the truth is you've really got no idea about a frame's history. I've seen lots of stuff on the internet, but the only 3 "real life" egs I've seen/heard of where there have been issues with frames/frames failings have all been steel.

If you're using some old school gas pipe, then yes it's tough and will last forever. But I find it hard to believe that for quality road/race frames that carbon / alu frames fail so much more than thin walled steel ones.