I played the game during the Early Access days, and back then the 'auto-buy' button included text which warned the player that enabling the function could potentially lead to bankruptcy. One of my gripes about the Beta was that this feature was 'dumb' (buying resources even when output is not profitable) instead of 'intelligent' (only buying input resources as long as doing so results in a profitable output). The release build/current build doesn't contain the warning text on the 'auto-buy' button, so I figured my gripe had been addressed.
Having turned auto-supply on by default in the options menu to try to streamline my experience, I noticed some odd behavior during a game. So I ran my own little experiment in a 1v1 skirmish on Applicant with rare resources. I built a robotic HQ, claimed all iron resources on the map without deploying metal mines, and built 3 steel mills. I immediately sold the steel as it was produced to drive down the price. Iron soared and steel plummeted. I turned the steel mill's auto-supply on without any iron in stockpile to see what would happen in this situation, and as I suspected the steel mills continued producing steel even when iron was sky high and steel had plummeted. My $10,000 starting amount was quickly evaporated by this 'dumb' button whose pop-up text no longer contains the bankruptcy information unless it is written in fine print somewhere.
Also, in the Almanac DLC included for Early Access members, the text states that the auto-buy button will only buy resources if the output minus input yields a net profit.
I'm not sure when the Almanac was written, but it shouldn't contradict the reality of the game. The fact that the warning text disappeared from the button makes me think the developers intended to make it intelligent but somehow didn't change the functionality from its original state. Some clarification would be nice.
Oh, and I also remember Soren telling me that 'auto-sell per resource would be included in the next build' during my 'Fundamental Critiques' rant. Having played the game more I understand why and when auto-sell may not be desirable, but was this feature nixed before the above referenced 'next build' during (late) Early Access?