When you’re going out to lunch or dinner with a business associate, a few basic guidelines apply. In my experience, it’s good etiquette to pay for the meal when you are:

– The person doing the selling, if the relationship is that of customer (or prospect) to vendor
– The person who invited the other one to lunch
– The person who added a bunch of colleagues to the dining party, if the original plan was for only a few
– The one who insisted on a very expensive restaurant (e.g. more than $25 per person)

Obviously, there are exceptions to these rules, and a lot of scenarios create overlap between them. Plus, many people would argue that the vendor-customer relationship trumps all the others. But if you consistently find yourself in a situation where you should have paid but didn’t when dining with a particular customer or other associate, it’s probably a good idea to pick up the tab next time.