So when you go to a sit down restaurant to eat, you wait for your server to ask you to tip them?

Your analogy isn't really appropriate. The fact is if a crafter clicks the trade button when there is no money in the interface yet, they are saying, hey here's the enchant for free. They can see if you've put a tip in or not, and they know that the click of the trade button applies to EXACTLY what is in the interface. If it goes green then it goes green. Now if you just sit there and wait for them to click green because you have no intention of tipping then you're a shmo, but that is a different issue, and now what this user is describing.

I think it is exactly what the user is describing. Say you go to Chili's and have some wonderful Baby Back Ribs. You finish your meal and the server gives you your check. In the WoW world the server just provided you with the service, opened trade and hit the trade button making the window green. They've already charged your card for the initial value. You can hit accept and walk out without giving a tip, or you can write down a tip amount and hit accept on your end causing the server to have to redo their end and hitting the accept button again.

I never accept tips- I charge fees. I have a few rare recipes among my tradeskills, and if I see someone asking for it, I wait 15 minutes before offering, and I always charge at least what I would charge for the product in the AH.

Well I guess it's a difference is culture then.
where I'm from tips are more exception than rule, usually I just pay what I'm charged and nothing more (to continue on your restaurant example).
And I know few examples of people giving tips (and I've worked in a restaurant)

Wow, I hope Elmo is not from the US. I've worked as a waitress, and they get paid SIGNIFICANTLY less than minimum wage because they rely on tips. I once knew a waiter with a table full of 15 or more people who all got up and left without leaving him a single tip. I felt awful for him- who DOES that? Even if a server is not as attentive as maybe they could have been, I won't let my husband leave without giving a tip, even a small one.

"Well I guess it's a difference is culture then.
where I'm from tips are more exception than rule, usually I just pay what I'm charged and nothing more (to continue on your restaurant example).
And I know few examples of people giving tips (and I've worked in a restaurant)"

And where exactly are you from? Douchebagville?

Tipping customs vary widely throughout the world.

http://en.wikipedia.org/wiki/Tip_(gratuity)

Note this is just a wiki article, but it's still enough the feel marginally edumacated about this kind of stuff.