If the server is able to tell they are faults I think they would qualify as obvious. If spot can't stop his swing he should hit the return into the net as he calls the fault. I don't think the rules are applied differently for high level players.
i often times think it is easier for the server to tell than the returner. the server has already hit his shot and can now watch it as he gets into position. the returner on the other hand is in the middle of moving to the ball and trying to get a good swing on it... and he has to process whether or not it was in. pretty difficult to do as a returner, especially if playing against a big server. i hit plenty of balls back and then call them out, and people do it to me too. not a big deal at all imo.