Seal immediately
Heat-shrink caps, self-amalgamating tape or the manufacturer's end cap applied at the moment of cutting prevent moisture ingress. Cable sealed on the day it was cut stays placeable for years.
Photograph the end
A close photograph shows whether the end is capped, taped, open or frayed, and whether the conductor is oxidised. That single image answers the buyer's main question about the reel.
State the remaining length
A cut reel's value is its remaining footage. Say how it was measured, and do not present the original length as current.
Expect a condition note
Cut ends are disclosed in the offer, not hidden in it. That protects both sides if a later inspection finds moisture.