I took a look at the advertisement. Purdey's name has brand value level one (BV1). The gun is obviously an Original Quality Grade one (OQ1). It appears to fit to the description of "heavy use, but no abuse," which is Current Condition level four (CC4). BV1-OQ1-CC4 = $15,900. For BV1-OQ1 (which for a Purdey best SLE were fixed at birth), CC5 (restored) = $12,000 and CC3 (significant use) = $21,000.

The gun is relatively fairly priced per my market model, but that doesn't make it what you want or right for you. Your best buy is most likely to come when your head and your heart agree on the same gun. There are plenty of really fine guns out there, so take your time and learn what you are shopping for.