Train tickets are generally non-transferable so, absent a black market, they are not liquid at all.
Actually, the tickets are refundable. There are restrictions which vary according to each train company (you might have to pay a small fee, etc), but still the tickets aren't completely illiquid.
Actually, the tickets are refundable. There are restrictions which vary according to each train company (you might have to pay a small fee, etc), but still the tickets aren't completely illiquid.