Yes, you're at the top for "Smiths Cheese Shop in Aylesbury", but are you at the top for "Northumberland Cheddar" or "Mail order Cheese"? Being "at the top" doesn't really mean a lot; what matters is how many people are finding you when they are searching for your product.
The new buzzphrase which is a bit more relevant to online search is "the long tail". Picture this: in 1980, a small bookshop could carry, say, 5,000 titles. Book shops focussed on best sellers, to raise the odds that customers coming into the shop would find what they wanted and buy it. But what they couldn't do is meet everyone's needs. And if 10,000 customers walked through the doors each wanting different titles, at least 5,000 would be disappointed. It's a different situation now. In the online world you can stock a million titles in your catalogue, and perhaps service those 10,000 difficult people who each wanted a different book. Which means at least 5,000 more sales. This - more specifically the long list of book requests - is the long tail:
The long tail goes on further than I can show... and that's the point: it's long - making up many more book sales than all of the popular books put together.
The long tail in internet search works in the same way. Of the 50 people searching for your product today, you can bet that, while 5 people will type into Google the phrase you expect them to type ("Smiths Cheese Shop in Aylesbury"), 45 people will each type something different ("Fine Cheese", "Oxfordshire Cheese", and so on, making, in effect, 46 different searches for Google to match up with relevant web pages).
Do you have 46 web pages which are relevant to different search phrases?
If not, it's time to give it some thought. Your next 45 customers could rely on you doing a bit of work on expanding your website!