I have an issue with when i start my third line and i had good couple lines going the bank account just went really quick this was after i already had my third line operation. Dont know if this was a glitch or i am just bad at the game.
I’m not sure what the problem is but it would be great if you could upload your savegame as mentioned here.
When saying that your bank account falls very fast after getting a third line to work it sounds like periodically selling. If you arrived at that point when your car stock is building up over time without selling any car no matter what Premium/Discount you set than it is the same as mentioned here.
So taking a look into your savegame could be helpful to check what’s wrong …
if it helps, the whole ‘periodic selling’ issue should be massively better in the next build which has a more realistic financial model.