When you put your analytical mind into gear this is when the channels shut down. All of these things go through our minds and it starts to race, then the doubts set in and we get upset, and do not want to discuss it with anyone in case they feel as if we have flipped. All of these things go through our minds. This is natural until we build up enough confidence to believe in our own ability to feel the difference, with the different energies that are around us. When our guides are close, there is a lovely energy.
Some people get hot, others get on a real high.
If the gut feeling tells you it is no good, listen to it. Another way to tell if the guide is good of bad is, I feel, that if a spirit guide is good then they will not use the instrument while you are low in energy or are not well. If a guide does not respect the instrument that it is channelling through, then do not allow it to come through. Ask your gate-keeper not to allow anyone through that is not for your higher self. Remember that the choice is yours at all times.