First CA-1-B16 - what to look out for

That one is in a very nice condition! The price is a little high, being it's in unknown running condition, however that is better than "known non-running" condition. I would try to talk them down to about half of that to be honest.

There is a lot of info on our forum here. Look for info on checking the crankcase oil heater, first of all. That is a critical part of the machine and can lead to the compressor seizing up if the oil heater is not working. 

Once you get the heater working, allow it to warm up overnight before starting the compressor. 

The CA machines use a low-pressure refrigerant called methyl formate. It is one of the most difficult refrigerants to obtain, and there are very few if any proven and tested substitutes which are not also equally difficult to obtain. For that reason, be careful of the lines and be sure not to break any during transport. As you have probably read, the cooling unit just sits on the cabinet, by gravity. Any tipping of the machine will allow the top to fall off, damaging the lines. 

Once you get it home and see what it's doing; we can give more troubleshooting advice.

Sincerely,
David

I think you're making a wise decision.  The seller may be a shyster, or may be just mistaken - but you can NEVER trust a non running example of a CA no matter what narrative the seller gives. You got to remember many are just out there to make a buck, or cut their losses. That CA looks to be in great shape and I expect it has been in service until something went wrong. It even looks plugged in, in the pictures in the CL ad.  

CA's are very predictable in how they fail. 

The most likely true story is, that they used it for years, without ever taking care of the heater or purging NCG out of the system. It seized up and they know something went wrong. They are trying to maximize their money when the sell it; by insinuating that there is little to nothing wrong with it. They have probably called around and been told it can't be fixed.