There are addons and macros allowing players to outright see a Wild Pets quality in-battle rather than guessing based on statistics - which in later levels can be quite daunting. In patch 5.1 these won't actually be required as Blizzard is implementing it as an in-game feature itself. You could
consider it to take away a small amount of fun from Pet Battling but alas, it's all for the better.
Wild Pet quality, though, is determined when the Wild Pet(s) spawn. It's easier to notice when a group of them spawn. Examples are things like the Alpine Foxling in Kun-Lai: where it sometimes spawns and has 2-3 Alpine Foxling Kits following it. If both (or more) are able to be Battled then you will notice that they both have an Alpine Foxling and Alpine Foxling Kit, as well as a 3rd pet - but that all 3 pets with have the same quality regardless of which pet you battle. So if you accidentally killed the pet instead of capturing you would have that 2nd chance immediately after.
The above statement can also be true of other Wild Pets that don't appear to be grouped but in some cases are. This is my experience anyhow