A well maintained (and designed) mold is key to producing consistent, high quality injection molded parts. Uniform cooling throughout the cavity impression (and from cavity to cavity in multi-cavity tools) will yield the highest quality part and the fastest cycle time.
Ensuring a quality mold requires well-designed tooling and higher precision build, both of which can increase the tool construction cost and regular maintenance cost. However, these measures will ultimately save you significant costs on repairs.
As a best practice, choose a molder that performs maintenance, such as cleaning parting lines during the production run, and has a dedicated service team that documents and tracks mold maintenance, to ensure that your tooling gets the long-term care it needs.