There will be roughly 3 phases of trade after the collapse.
In the first phase, 0-5 years post collapse, survival supplies are going to be the most in demand. In this phase, precious metals won't be worth much yet, since they don't have any practical survival value. Also, not everyone has the knowledge about precious metals to estimate their value. Honestly, if someone brought a gold chain to me, I wouldn't know how to test it or value it. I don't know much about carat and karat. Plus, not everyone is going to have a scale. (Helpful tip: get a scale now and you could be an important trade authority post-collapse.) However, it all depends on the person you're trading with. Some people will strictly be in the mindset of survival supplies are all that matters, while others will already be engaging themselves in precious metals trade. In the first year, you will even be able to find people that will still be using paper currency, because they are holding on to the belief that governments will reestablish themselves, and they want to be rich when that happens.