How do I tell if a used bike (craigslist) is worth it? So there are always a lot of sales going on on craigslist / ebay / etc. How do I tell if what they are selling is worth it?

I don't really know the difference between a $500 bike and $1500 bike. I know weight is one of concerns but 20 or 25 lbs or even 30 lbs it's pretty hard to tell the difference. There are multitudes of brand names and even more variations within the brand name. 

There are also the group sets (even discounting too much of customization)

My stats: 5'10, 270 lbs
Purpose: Commuting ~12 miles daily (each way) - (assuming for long rides 50+ a hybrid is better)  

I am planning to go to a local shop to try out some bicycles but, i also don't mind used, but somehow doubt someone from Craigslist will let me do a 'test drive'. Hopefully this is enough information about what my purpose and question is



to sum it up:
- What should I look for that will make the difference between a $500 bike and $1500 (both for same purpose) when it comes to Frame/Components
I would say that most people on Craigslist would be willing to let you give it a test ride, I mean it's similar to buying a car. Just, as I always tell people, meet with the person in a very public space. Much safer place.

As for what to look for, I would do a little research into exactly what you are expecting to use the bike for. Figure out the kind of bike you need and do a little research on the kind of mech recommended for what you're doing,(frame, gears, wheels, shifters, brakes, drive train.) Once you figure all that out, you can narrow down your selection on Craigslist. Just like looking at different models in the store, online you will find pictures, descriptions, e.t.c. So you can find the right bike for you.

Once you think you've found one, speak with the seller and find out more about the bike. Research things like the bikes brand, how old it is, e.t.c. Once everything checks out, boom. You have your bike!