The idea that Germany would hold back useful rifles at the end of the war for parades is as silly as it is plausible. You'd think they had enough good looking SS men with issued rifles from the last six years of war. That said, GI, Tommy, and Canuck veterans would have scooped every good looking rifle for their collection or conversion. Surviving eight decades without creating a legend is very unlikely. IMHO, that one looks too new to be as is from 1945. I agree it must be a postwar rework.
I've spoken to people, REMEs whose job it was after the war to round up an collect Axis small arms. There were piles of them in every village square and throughout cities. Often, in the field where surrenders occurred in large numbers, the bolts were thrown on one pile and the rifles on another.
I've heard stories of many of the weapons being left out in the weather for a couple of years after the surrender.
In some cases, they just dumped them into pits and buried them.
On many battlefields, they didn't even bother to collect the bodies or the weapons and just threw or bulldozed them all into the trenches they fought in or pits they dug later to get rid of the bodies before disease started to spread. Times were harsh.
I spoke with one fellow who told me there were both small and large warehouses with crates of firearms and ammunition, new, or ftr which hadn't had time to make it out for redistribution. There were all sorts of facilities to do field repairs and in some areas, complete FTRs.
I agree that rifle was put together post war from a new unassembled receiver.
That polished butt plate is a dead give away, as is the stock and even more so, the condition of the receiver. Such a late war produced receiver would normally not be finished to a luster and would usually be full of machine marks.
$1500 may be a bit out of line for that rifle but that premium could be called for as all the numbers are matching. If the bore is excellent as well, your price was top dollar, but fair.
From your photos, the stamps on the top of the receiver look "light" which happens when those "rough" receivers are refinished.
Nice looking rifle. Don't be afraid to shoot it, with commercial ammunition, made in North America. It's loaded light.
Not that I would be worried about that bolt or receiver.
Many of those rifles were FTRed post war for military, border police, and police units. Some had all of the stamps scrubbed and "tng" stamped
Others were assembled on NOS receivers, which were void of any stamps.