Provide information on sample preparation. Give protocols, tips and what common mistakes should be avoided.
Establish standards ways for preparing samples and standardised reagents (SOPs). Test for contaminations and quality. Use reference samples/reagents.
Motivate the user to follow your advice by giving examples of good and bad samples and their consequences.
Once the samples are ready for experiments, they should be checked for quality before proceeding any further. Bad samples should be redone. Discuss with your user how sample can be improved.
In case of insufficient quality, CFs should discuss with their users (PI) what consequences the sample quality will have on data interpretation and if the experiment should continue. Discuss the drawbacks of using poor samples in case they cannot be redone.