If it werent for walkthru guides, and if it was your 1st time playing, how would you know if they were really the traders or not. I think the creators made the encounter with the 1st time player in mind. On a table top, you dont have saves to go back to and try different scenarios, you get 1 chance, thats it. The only way you could know they are really the traders for a 1st time player, without the walkthru, is thru conversation. If you really play it like roleplaying, there is one shot, no restarting, no looking at the walkthru to see what to do. I think this was the intent.
I know because AFTER i did the first try I looked it up on this site to see what was what. As far as your assertion about tabletops game go, I would say id ambush the enemies and then return to town, get arrested and then tell the Constabulary to go F itself, refuse to cooperate and thus make them kill me. Then after the session was done, If i didnt just walk out or rage at the GM, Id ask what the F he was thinking. If the GM then explained it we'd be right back where we are now.
How would you know if they were really the traders or not? At the start of the quest you are given a full detailed dossier on the entire group. When you encounter them with the children, you can see that they match this description perfectly. There are seven total, with a charismatic female sorceress, a cleric by her side, a fat rouge, etc. Now I suppose that they COULD have been rescued by a group of seven people who match that description by extereme coincidence (1 in 100,000 chance or whatever), but it's pretty obvious that it's them. Seperately, I was always curious why a group of 16th - 20th level powerhouses are bothering with traficking a few slave kids, when given their collective might they could be conquering the known world.
D&D by it's very nature of levels is full of contradictions like that. For example, the Verbobonc regional patrol - level 10 fighters to a man, with high level battle mages and the force of the high level clerics of the church of Pelor in Verbo backing them up and the triplets as shock and awe frontliners or mopups - could easily wipe out the Temple uprising in short order. If you're going to have high level content, you have to have higher levels in general.
Given the approach you've described to the encounter, I'm surprised you didn't select "skip to the fighting" without any prompting.