>>1234978>carbon, aluminumDon't bother unless it's cheap and has a good groupset that you can strip and ebay. It's impossible to tell if frames made with either material are 100% intact.
>steelGood steel usually has a sticker on it indicating the tubeset (e.g. Columbus SL, Reynolds 531, Miyata SSTB, etc). Look for cracks around stress points and joints. Pay attention to the bb. If you're serious about it, pull the seat and shine a light down the tube looking for rust.
>tiTends to crack around the welds.
>groupsetsIn vintageland, cottered crank = shit bike. Until around 1984, Suntour>Campy>shit>Shimano. Then Suntour's slant parallelogram patent expired, and Shimano took the design, came out with SIS, and ate both Suntour and Campy for lunch. Suntour friction was still the best, but in indexing world, Shimano beat everyone. If you're looking to flip components, Suntour Superbe Pro still commands a big premium on ebay, regardless of year, as does anything Campy. Shimano generally isn't that desirable, except for Arabesque.
If you're looking at 90s and newer bikes to ride, play it safe and stick with Shimano 105, 600/Ultegra, and Dura Ace. Note that STI shifters back in the day had a habit of gumming up and grenading, particularly the right lever. Shimano 10sp can be dodgy, as their first attempt to route cables under the tape was fuckawful, and their second attempt was better but still not great. They sorted their shit out with 11sp, but make sure to peek into the levers and see if the cable is frayed. It's a design flaw with STI that they're apparently never going to fix.
Late in the 90s, Campy more or less sorted their shit out and came out with some great groupsets, but these days hard to find parts for. I'd stick with 9sp+ Chorus or Record. If it's 9sp, it can still be upgraded to 10sp by Branford Bikes in Seattle. 11sp is generally good, except for early 11sp Super Record, which you probably won't see at a big used bike sale anyway.
