I would tweak your model just a little bit. I think splitting the bill is a nice default, but if someone wants to pay for the dinner than they should be allowed

I would tweak your model just a little bit. I think splitting the bill is a nice default, but if someone wants to pay for the dinner than they should be allowed to without violating social convention. If I suggest dinner with a friend, when I know they would probably not be going out for a meal, I'll almost always pay for both of us. if it's more of a mutual, "yeah lets try that new Greek place" type deal, we'll usually split. The same applies if I approach someone and offer to take them out. It was my idea, I'll take care of the financial responsibility, especially since I chose the venue (which could be dramatically more/less expensive than the other party would want to pay). I think online dating might be a good model for splitting the bill because both parties are entering the situation ostensibly looking to go out for something. Additionally, when I pay for dinner, most people graciously accept and then suggest that they'll buy the first round of drinks or ice cream or whatever we might end up doing afterwards.