Is your feature request related to a problem? Please describe.
Send a redstone signal when the trade station completes a trade. This can help players dump useless villagers and leave useful ones.
Stop trading when the trade station receives a redstone signal. This can prevent excessive losses when the players just use a trade station to test whether a villager has a certain trade.

Describe the solution you'd like
Trade stations send and receive redstone signals.

Describe alternatives you've considered
None probable.

Additional context
None for now.

Sure