Leave Growing Room
Let's talk about the size of herbs when you buy them. You are already getting great value when you buy a herb growing in a pot - the more you cut it, the more you stimulate new growth. Unlike dried or cut herbs - which, once used, are gone.
Herbs will grow to fill the size of the pot or space you give to them. I buy mine (on the rare occasion I do not grow my own from seed or a cutting) when they are small. This means there is still space in the pot for them to grow. It's very tempting to buy a plant that is already rich with foliage. It looks bigger and healthier, but that necessarily the right way to go, when you consider the fact that its roots may already be struggling for breathing space. So when you buy herbs, buy small(ish) and let it flourish in your care.
Consider the Seasons
During the Autumn and Winter, plants will be smaller, many of them entering a dormant state. So, in lots of cases, you won't be treated to as much delicious foliage. That's why I sell my herbs at discounted prices during these months. But then, once the Spring and Summer hit, they just flourish! So your small investment during the seasons before, pays dividends.
There are some who do pay for large pots of large herbs in the Summer, and that is fine. But if, like me, you are always on the look out for a bargain, go for smaller, cheaper and out of full 'herb-flourishing' season. For the most part, your little herbs will be easy to keep during the colder months, if you follow the instructions for doing so.
Here you have, going from left to right, lovage in its pot as a small herb, in a bigger pot, and in the ground. Each grows to fill the space it is allotted and it grows quickly once the season is there for it to do so!