One way, (I am being a tad facetious), is to look at the firing pin indention on the primer. If it is anywhere near the center, something probably has been done to the action.
If the barrel is out of the action, look at the action face. Remingtons have a cross cut ground finish, any truing should appear to have a single point tool look.
As others have said, just looking at lugs, bolt nose, etc, can give good indications. But, as has also been said, you really have no idea what sort of "truing" has really been performed. From a machinist standpoint, many so called "truing" leaves the action in no better shape that it was, and if by truing the timing and promary extraction was all screwed up, the action might be in worst shape that in the beginning.
All sounds bleak, huh. But unless you know who trued it, and what procedures were used, just do not assume that everything is as it should be.........jackie