This is actually incredibly difficult to do in our society where we always have to have the best or the newest. In addition it is difficult because we often need a bank loan to buy a house or car, which are fairly necessary to function in the world we live.
It is admirable to stay out of debt, but even if you are dealing with some debt there is still hope. By making her dealings profitable, she is also not living outside of her ability. There is a difference to buying a reasonable car to fit the needs of your family and buying a ridiculous car that is far above what you would be able to pay a month. So a profitable dealing could be as simple as staying within a budget every week or month.
I also believe being profitable has a lot to do with attitude. If your attitude stinks then your dealings will stink too. By keeping a positive attitude and lifting others up instead of breaking them down leads to the best profits you can have -- righteousness in the eyes of God. He will look after you in all of your dealing, the best you can do it keep your noble character and know God will take care of you.
The phrase "her lamp burns late into the night" is a dangerous one. This doesn't mean she consistently stays up all night and burns herself out on work. It does mean that she has good time management and does what is necessary to get the job done.
Psalms 127:2 -- "It is useless for you to work so hard from early morning until late at night,
anxiously working for food to eat; for God gives rest to his loved ones."
Working yourself to the bone is not helpful for anyone, and it is not what God wants for you. God wants to grant you peace and rest. This means getting things done in a timely manner and staying on task. In other words, the wife of noble character is a good manager, especially with her time.