We currently have OUTDOORSMAN CHECK on every encounter. Which means, that if you can avoid encounter via dialog, its just BONUS from your high outdoorsman skill. So it sounds logical, to simply set: "always avoid" or "let me choose", or "always enter".
Guys, as Michael said: If you see dialog, you SEE whos in there. So you can avoid him (even without clicking, you need to just wait till some timer expires).
Its like this:
Travel, travel, travel, than suddenly i spotted group of merchants! Im hiding behind trees, and they dont see me. I get the message. I can leave area, or meet them.