Even in a private sale the goods delivered must match the description. Where the condition differs noticeably — worn gold plating on the cap ring, a cap that wobbles perceptibly although it seats firmly, signs of corrosion on the rings, or deep scratches — the buyer is entitled to unwind the sale. The first step is a friendly but firm word with the seller; in practice most give way when the description was demonstrably incomplete. If that leads nowhere, online auctions have the platforms' buyer-protection schemes, which cover purchases up to a certain sum.
The term “as new” is to be read strictly. Anything not still sealed in its wrapper picks up the faintest of marks sooner or later, even a pen bought in a boutique; visible wear, scratches or technical shortcomings are not covered by the phrase, however. With common models, returning the pen is almost always worthwhile, because re-plating or repair costs more than buying a better example. To avoid disappointment, it is better to buy used pens from a specialist dealer or at a pen show, where the condition can be checked before money changes hands.