I haven try replaying the same mission so I dont know if we could earn the credits over and over again but how do you spend your credit?
so far I bought the turret for bunker only... The best defence is offence

hmm... i think i got it wrong
the turret thing is suppose to be that zerg research thing
I bought that add 2 units in bunker i think

That Protoss and Zerg research thing can choose 1 out of 2
but the credit ones buy anything you like

Can the credits be earned if you redo the mission?

I played war hammer and they allow it. Nvm... tonight try and c
what if play on other modes such as casual, normal, hard, brutal

Marines are given free
wonder why firebat are not available in multiplayer
I tried carrier rush against easy enemy and very easy enemy
still very noob

I definately wont spend any credit on mercenaries. in game still need mineral to deploy them... FTW... double payment

I'll keep the credits till i fail mission then only c which to buy
so far still ok... finish 7-8 campaign only

I confirmed that credits cant be earned twice but the research points can be recollected. Eg in a campain there is 3 points, you collected 2 and finish the game, you can reply and collect all 3 to get that remaining 1 point you left previously