Evening all.. I was having a look a a vintage bike that had Campag gearing as OE but the owner has sold them and replaced with Tiagra gearing would that knock the price down?
When weighing up an old bike, think about what sort of quality league the frame is in and what sort of component level you would expect to have been fitted when it was new. People rarely saved up to buy high quality frames then fitted cheap mechanicals.
It's very common for people to buy a nice vintage bike just for the mechanicals, take these off, then either resell the bare frame by itself or fit the frame with cheaper bits they had lying around before resale.
When I see a bike that has poor condition mechanicals, or lower budget mechanicals have been fitted in place of more expensive ones, then I assess the value of the bike to be the value of whatever quality the frame itself is and not a lot more than that. Two of my 531's were acquired on the basis I paid what I thought just the frame was realistically worth and any mechanicals that turned out to be in useable condition was a bonus.