Good question since actions are often worked on by owners or even overworked by a gun smith.
You should know you're pulling the trigger in double action but it shouldn't be excessive plus it should be very smooth.
Single action is light to the point of dropping the hammer with just like pressure.
A test I do is I cock the hammer then push on it to see if it drops without pressing the trigger. if it does then there's a serious issue with the action.
It sounds like the gun may just need a good cleaning at least or at most it will need to be looked at by a reputable gunsmith.
Put it on lay-away and let us know how it goes
Regards,
Kobsw