Not long ago I purchased a 1950s, steel-cased, Girard Perregaux Sea Hawk from one of the more well known and well respected sellers on Ebay. It was listed as: 1. original; 2. keeping accurate time, having just been serviced. Visually it was in great condition, with untouched dial, yet on a new strap.
Upon receipt, I discovered it was running ~10 minutes slow per day. (yes, minutes.) I wasn't too happy about it, but realized that things do happen, and didn't really 'sweat' about it. I reached out to the seller, who was quite accommodating, indicating I should send it to his watch maker. I did. Within a week I received word the main spring was being replaced, would be timed for a few days, and shipped back to me.
I opened the box today. Visually it looks the same, except the original winding crown has been replaced with a brass colored, "JJ" (Jules Jurgensen?) crown. It clearly is no longer original. I wasn't aware of this swap until I opened the box.
Even if it now keeps strong time, as it was originally advertised as: how would you react? A good part of the allure for me was that it was an original piece. Now it's a visible franken-watch, with a crown that doesn't even match the color of the case.
Thank you for your feedback.