The engraving is not bad, but the discrepancy between the well worn grips and the fresh looking engraving suggests that the gun was engraved at some considerable time after manufacture.
Not having actually seen the gun, it is difficult to evaluate it. But as a general statement, there has been a practice, primarily in Europe, of buying old guns (usually pin fires and the like), having them engraved in areas where such work is cheap, and then selling them at a huge markup. I have seen old Belgian pinfires so engraved, gold plated, and put up for sale at €5000 or more, sometimes with stories about ownership by royalty. And younger collectors with more money than experience buy them.
General thought: How do you make a rusty and worn gun with no original finish worth many times what it is? Easy - you have it engraved.
Jim