Can you have negative profit in the stalk market, or does it 'bottom out' at zero?
I used to do a lot of Stalk Market trading and there were other people who were doing it and and we spent a lot of time calculating profits and costs etc.
Basically losing money doesn't affect anything. Whenever you buy and then sell for higher, that profit goes towards the achievement. If you ever incur a loss that doesn't affect your your profit. If you made a profit of 50 then you lost 500 and the you made a profit of 100 the game will have it as you having made a profit of 150.