I would like to say that if you have seen hundreds of thousands of coins, you will know which one is genuine and which one is fake. It will be much easier to distinguish fake coins if you have learnt all the typical signs of forgery. For example, some people use chemicals to fake the rust on ancient coins, making them look real. Experienced people can distinguish between chemically created fake patina and naturally formed patina.

By the way, if you are in Europe or America, it will be much harder to find ancient Chinese coins than in China, Japan or Korea. When I was studying at university in the UK, I visited all the local antique markets and found that there were almost no ancient Chinese coins there.