Everybody seems to think they are the worlds greatest spotter. I have been wheeling for way over 30 years and I trust only a few people on the trails we run. I mostly get out and look, plan my line and then make everybody shut up.
Very few people, even seasoned drivers can spot well. You have to have enough experience and four dimensional visualization. You have to be able to judge distance and if one tire is in one spot, where will the others be, along with the CG and then plot you next move. Like chess you need to think many moves ahead.
I have been in a spot where due to the fact it was the middle of a moonless night and how vertical the spot was, I simply could not see. My lights were blinding my spotter so I had to turn off all my lights and blindly follow commands. This obstacle required placing a tire exactly on a particular spot and if you didn't you were going to barrel roll down the mountain. Talk about trust. The route required putting a tire about 4 feet in the air and then teetering over until the opposite tire was that much in the air.