I certainly wouldn't buy a second-hand cot if it was that old. A newer one, maybe, but not an older one. As I said, cots made before about 1985 generally aren't safe.
The two things that should especially NEVER be bought second-hand are helmets and car seats. There are two reasons for this. First of all, they have an expiry date. (Yup, plastic expires!) Secondly, you do not know the history. If a helmet or car seat is ever involved in an accident it MUST be replaced, even if it looks okay. There could be microscopic damage that is too small to be seen, but could render the item unsafe.