I have personally watched hundreds of Bassos and Rossins being uncrated and reamed. Those are usually counted as better quality bikes and definitely brazed. They needed reaming badly. Have seen a new Hetchins that needed reaming. A new Colnago built for Eddy but sold when he switched to De Rosa that needed reaming. Some builders at the level of Chris Kvale build so precisely that Columbus SL frames might use a 27.4 but even in that rare air it is not assured every time. Reaming is normal. Big question is does the builder do it or does the store do it. If the builder expected the store to do it and the store is not prepared to do it anything might happen.

And then there are liners. For all sorts of reasons builders decide to use liners. I've never personally examined a seat bore on an old RRA, first guess is that for a frame built of 0.7 straight gauge in the 30s there were few if any seatposts available so they lined it for a normal post. But there are all sorts of other explanations for why rhm would have a light frame with a one inch post, my guess is only a starting point for an investigation of facts.

Probably half of all the top quality bikes I have owned came with an undersized seatpost fitted. Presume many here have had the same experience. Still there are collectors and perfectionists who have obsessively maintained bikes and no clue why that binder bolt is bent or why the post is stiff going up and down or why the post keeps getting so scarred. General public, average LBS, they just put a post in a hole. They come in different sizes?