What to look for when buying an old/vintage bicycle online

I've bought dozens of older, steel bicycles over the years. Most of them I've purchased used on Craigslist, eBay, or Facebook Marketplace. One thing I have learned is that you can *never* trust the pictures sellers include with a listing. This isn't to say that sellers are dishonest. It just means that photos typically can't show the true condition of a bike (for better or worse). 

Depending on your mechanical ability and patience, there can be some hard lessons when you buy a used bike sight unseen. Here are some general tips to help you evaluate if an older bike is a good deal or not worth your time and effort to restore to rideable condition.

• Buy the seller, not the bike. This applies to almost any item of value, really. If the seller feels wrong, or if the bike is not something they seem to have any connection to, walk away. I always check bikeindex.org to make sure something isn't stolen.
• Steel. Not all steel is created equal. Look for "full chromoly" labels. Avoid the "hi-ten" (high tensile) steels. They are heavier and not as strong. Occasionally you will find a mix of tubing, or a full chromoly frame with a hi-ten fork. These are still good choices; just make sure the construction is decent. Look for nice lugs or at least good welds.
  
• Rust. Some people are freaked out by it, but any steel bike is going to have a little rust somewhere. They key is to identify if it's cosmetic or structural. Remove the seatpost (you should do this anyway to make sure the seatpost hasn't become seized to the frame. If you can't inspect in person, ask the seller to do it) and shine a light down the seat tube. You should be able to see all the way down to the bottom bracket. A light coating of rust is NBD. You should still be able to see the silver metal beneath the rust. Rust that has caused structural corrosion is bad. If the rust looks like scabs, that's bad.
• Fasteners. This is something usually not checked until it's too late. Check to see if the little bolts holding the water bottle cage are able to be removed. Also check adjustment screws for brakes and derailleur. If they are seized, this can be bad.
• Cables. Are they frayed at the ends? Are there strands poking out? Not a deal breaker, but something to factor in for replacement costs. There is a big difference between "the brakes work" and "the brake cables could literally snap at any time."
• Bearings. Does the steering work smoothly with no notches or binding? Do the wheels turn smoothly with no side-to-side play? The older cone bearings are simple to rebuild, but you have to make sure the races are not damaged. If they are, this could mean new hubs, and would add a lot of cost to your bike. At the very least, you'll want to remove, clean and repack the wheel bearings anyway. This is an easy job, if just a little messy. Headset bearings need servicing too. Replacing the bearing cups in a damaged headset is not as daunting as it sounds. All of these issues are bargaining points. If the wheels turn smoothly and spin freely for 60 seconds on their own, you probably have something serviceable. 
• Spokes & Rims. Look for cracks where the spoke attaches to the rim. Check for wheel wobble, too. This can be an easy fix, but if the threads on the spoke nipples are stripped or corroded, you could be looking at new wheels. 
• Derailleur. I am listing this one last, although it's usually the first thing people check. Most likely, you'll see some scrapes from tipovers and crashes. Replacement derailleurs for old 7/8 speeds are cheap and work great. What you do want to look out for is a bent derailleur hanger. If it's slightly bent, this is an easy fix. Steel is a great material for bending things back to their correct shape.