When shopping online, most of us only purchase media from brands or manufacturers where we know for sure what kind of disks we're getting. Unbranded Taiyo Yuden (TY) is always the same media code, so there's nothing to think about there (except whether you want the Premium or Value line). The same with Verbatim-brand media (the media codes are always the same, although there's an additional indicator of manufacturer that can only be determined in-store). Whatever the speed, we already know the code. It doesn't change. Outside of those, it's pretty much a crapshoot.
Here is a list of media where the codes are stable, and you know what you're going to get, all the time, no matter what:
Unbranded Taiyo Yuden (always TYGxx in -R and YUDEN000xxx in +R)
Verbatim (always MCC xxxxxx in -R and MCC xxx in +R for Made in Taiwan media)
Hewlett-Packard (always CMC MAG xxx)
Plextor (see TY above)
Can anyone think of others?
Now, that was mail-order. At the retail level, here are the brands where you can easily identify what you're going to get, based on additional visual cues on the packaging:
Sony (Sony/Daxon-made have round spacers and TY-made have octagonal spacers)
Verbatim (CMC-made have serif fonts and Prodisc-made have sans-serif fonts)
There are a couple of extra issues regarding the above two, but that's just the basics. The point is, we know how to identify based on visual cues that we've picked up on for certain media.
One other thing, in regards to distinguishing between Premium and Value line TY media, the best rule of thumb is to only buy from Rima.com (they only sell Premium TY) and/or only buy TY from SuperMediaStore or Meritline that comes in cakeboxes. TY value media usually comes wrapped in plastic or tape packaging, whereas the premium media is usually only to be found in cakeboxes. Someone correct me if I'm wrong about that.
And of course, in case it's not self-evident, I'm in North America, where you are, but the rules may be different in other parts of the world.