The “Quality” of a mold can be looked at 2 ways. The tool lacks “quality” if there is a defect in tool making. The tool is built to a “quality” level based upon the budget and needs of the customer.
The Society of Plastics Engineers outlines mold standards from Class 105 to Class 101 based on the tolerances the finished part needs to achieve and the number of parts the mold needs to produce.
Each class has a specific list of features and characteristics that allow the tool to achieve the desired number of shots.
There is no difference in part quality from a class 105 or 101 tool. Errors in tool making that lead to defects in parts are errors in tool making not a reflection of standard to which the tool is built.
Class 101: exceeding one million cycles.
Class 102: not to exceed one million cycles.
Class 103: not to exceed 500,000 cycles.
Class 104: not to exceed 100,000 cycles.
Class 105: not to exceed 500 cycles.
When 2 tool shops in the same area quote on the same tool to the same standards the pricing is usually within a few dollars. The difference in quoted prices comes from one company quoting a class 104 tool and another quoting a class 102 tool for the same part.
The quality mold tool should be the one that attends the customer requirements. There are many kind of injection molds. If you need a short cycle it must have conditions to give you a short cycle. If you need good surface quality in your product, the tool must be done with good steel and must have a good polish or treatment. In fact your question is a little bit subjective.
The good quality of tool depends of your expectations, and you must specify it when you are buying a mold.