When serving tea it is important to use the right amount of leaves. There are no hard and fast rules as it differs greatly from tea to tea and for different brewing methods, but in most cases you need less tea than you think to make an infusion the correct strength. The length of infusion time makes a big difference to the flavour, and a small amount of leaves can go a long way.
If you use too much tea, you will find the flavour of the infusion to be sour or bitter. Of course, if you don't use enough tea then the flavour will be weak or thin and the infusion will be underwhelming.
For the purposes of catering and hospitality it is worth following the general rule of less is more. An average heaped teaspoon of Breakfast Blend will often be enough for a single pot (say, 250ml). It is worth noting that a pot of tea for two will not need twice the amount of leaves. If an infusion seems weak then it can always be allowed to steep for longer. Tea by tea you'll get to know, and we'd recommend you trying out each tea before serving to customers to help you get an idea.
Exceptions come when brewing teas in different styles. For example if you decide to offer some tea options made in the Gongfu style, you will need to use a lot of tea for the small size of the pot. This is offset by the way that Gongfu style teas lend themselves to re-infusing, though.