Nowadays, invitations often carry a "regrets only" notation at the end. That means that the host will count on your being there unless you tell him or her otherwise.

We should feel obliged, therefore, by your acquainting us, as early as may be convenient, whether your company either have or are disirous of having an agent here.

We could tell you a lot more about RELIANCE tyres, but would prefer you to read the enclosed copies of reports from racing car driver, test drivers and motor dealers and manufacturers.