Even an "old war horse" could be worth a lot more than $400, if it is correct. The vented handguard is not original, but that may be the only thing wrong with it.
In any case, just about any non-import GI M1 carbine is worth more than $400.
Unless it is truly trashed and import marked, I would buy it...quickly.
Still waiting for my Flashback...I would like it now, please.