Ive found something interesting. You can use the great hammer part on the One hammer tool and the customer's will accept it and give you the price of the great hammer even though they asked for a normal hammer. Makes it more worth to get great hammers instead of normal ones.
A really good tip if you are doing this legit is that every night, instead of instantly going to bed, stay awake as the timer wont change and nothing will happen to you if you do stay awake, the game will only resume when you sleep. In this time, what i usually do is to make every part (Hammer, dagger, swords) and order 5-10 of every grip handle and some excess ingots so that the next day, i just need to assemble the tools and give it saving so much time.