I pretty much take cues from the client. If he drinks heavily, I do as well. If he orders water, I do as well.

Again, you control cost by selecting the type of restaurant...be prepared for some clients to order from the top of the menu even if many people consider this tacky.

If I am the one being invited, I do everything in moderation, and the host usually follows suit.

Usually it is pretty clear who is paying before the event.