I do not necessarily believe that Tam was a warder, but to play devils advocate.... One of the major arguments against is that Tam would have sensed the Trollocs. Didn't he put a lock on the door (which Rand had never seen him do before), and go upstairs to get his sword? But this could also just be from hearing about the boys seeing the man in black watching them. I think he may have known it was a Myrdraal. Maybe he has had experience with them before. I was never quite sure why they went back to the farm that night. Maybe he wanted to protect his farm. But he would be leaving for the festival again in the morning!? Maybe he suspected a myrddraal and wanted to have a sword handy, thus he had to go back to the house. If not a myrdraal I think he suspected shadowspawn. I will look up quotes another time. Just thought I would provide more fodder for "discussion"!