Again, you're assuming a per-label consistency that just isn't there. Riccardo Chailly's Mahler 3rd on Decca is miles ahead of some of the multi-miked messes of the 1970s. That's on recording quality alone. Performances were and are all over the board for Decca (and any major label).
Here's what you need to do: spend some time and learn which conductors shine in which repertoire. Karl Böhm's Mozart is pretty uniformly wonderful, but his Wagner might not be to your liking. Moreover, learn about conductors' own styles in general. Otto Klemperer can turn in granitic, monumental performances or things that seem leaden and arthritic - and it depends on your own opinion.
Learn which orchestras do well for which composers; the Wiener Philharmoniker is hard to beat in the central Germanic repertoire, but there are those who say that they're no good for Mahler. You should consider that, and plenty of similar examples. Moreover, see which orchestras you like overall. If the Staatskapelle Dresden or Cleveland Orchestra tickles your fancy, just as two examples, then it's a good bet you'll like their sound in more than just one instance.
Learn the "house sounds" of the various labels - some of which change pretty wildly over time - and decide what you like and don't like. A Deutsche Grammophon bright, close, and spot-miked extravaganza might not be to your taste, and it might be the ticket. See if you prefer live recordings or studio sets.
I doubt that's terribly helpful, given your stated desires, I'll just say this:
The Deutsche Grammophon, Decca, and Philips "Originals" series (it was Decca "Classics" before the big UMG standardization) are usually good performances in decent sound. They're cheap, too, even in their retail incarnations, as they're bargain releases of classic records. DG's "Grand Prix" series is up there, too, but I'm not sure how many of those would be making their way to the used market so soon.
You asked how to eyeball a record and know if that's the one. You need to familiarize yourself with the above, i.e., paragraphs 1-4, otherwise you'll be shooting in the dark.