Another factor you have to think of is this: Now that there are so many "webmasters" out there...there is a great possibility that the traffic you are sending has already been there through another affiliates code. And if they have been there already they are cookied with that code and the original webmaster gets the sale. I see that happen a lot. Hell, I'm the recipient of a lot of that kind of love.
That's why I always try to be the firstest with the mostest.