Add up everything that leaves the account in a normal month — rent, insurance, subscriptions, fuel, materials, your own wage. That total is the only number that matters, and most owners have never worked it out.
Write it somewhere you will see it. Now every quote, every quiet week and every discount has something to be measured against, and you find out you are in trouble in week one rather than week four.
Businesses rarely fail because they were unprofitable. They fail because the money arrived later than the bills did.