Starcraft – can’t earn ‘Cooperative novice’ in sc2

At first, the credits available to you in the single player campaign is limited to that from missions alone. However, once you've fully maxed out either the zerg or protoss research trees, you gain the ability to trade any future research points into 10k worth of credits.

There have been mentions of a glitch with the way the game handles this: if you replay a mission you've already beaten and acquire protoss / zerg research points within that mission, it is possible to get the Moebius foundation to "purchase research samples" from you, even though you failed to increase your net points (you already got them once). In this way, you can accrue as many credits as you need, and can buy all the armory upgrades in a single playthrough.

Update: This method has since been patched.

As of now, the best way to earn the armory achievements is to play the campaign multiple times, selecting different upgrades on each playthrough, as achievements are shared across all campaigns.

One approach - which could probably be deemed cheating - is to play on the map Burning Tide. The goal of this map is to be the first team to collect 15,000 minerals.

You can get all the Outmatched achievements this way, because the AI players spend minerals on units and buildings, yet they do not attack. The AI players also do not collect the minerals deposited by the lava - this becomes important when going against 3 or 4 AI opponents.