Okay, I see where we are talking past each other. My point wasn't about the bad motives of anyone who makes this mistake, just that I disagree with the Cosmo
article which says guests should
tip at open bars. I'm sorry for being misleading if that's what it seemed like to you.
The point is this: customers (in the case of a wedding, that's the hosts) tip. Guests don't. No matter what their motives.
Returning to my analogy above, if you were invited to a dinner party at someone's home, and they had hired someone for the evening to help with serving and doing the dishes, would you tip that person? I hope not. It really would be out of place. If I were your host, I would be really irritated, the same as I would be if you "helped" me by going into the kitchen and "fixing" the seasoning of the food that I was going to serve. It's one thing to offer to help, quite another just to go ahead and take it upon yourself to do it. Well, the same is true of paying the helpers at someone else's home: I suppose you could offer to contribute, but you don't interfere with your hosts' planning and just go ahead and do it. The fact that your motives are nothing but the best doesn't change that.
Similarly, if your friend treats you to lunch for your birthday, you might offer
to leave the tip. But simply to leave an extra tip on top of what she leaves for the server would be rude. Again, the motives are irrelevant.
And a wedding reception, like any other party or hospitality, is simply an extension of the same principle. The hosts, not their guests, pay, including the tip. Guests stay out of it.
that is the way it is, for a guest to violate that convention by tipping looks odd. But the point isn't that it will necessarily be taken as either an insult to the hosts' generosity or rudely trying to buy superior service -- it could also just make the guest look clueless or perhaps conforming to a foreign system where tipping by guests is
the norm. Or that they have been reading Cosmopolitan