As a technology transfer centre, we have been conducting COSMIC estimation methodology trainings for several years for organizations from different domains. This paper reports about a retrospective look on these trainings, which highlighted a number of recurrent issues. Some of them are related to the COSMIC method itself or to functional size measurement in general, while others have their roots in other fields like project management or requirements engineering. Failing to address those issues in an adequate way may prevent from meeting the training goals and successfully adopting of the COSMIC method. We also report about how we have designed our trainings to integrate most of these issues and to capitalize on returns from trainees. In the following, we explain some of the most recurrent ones and give some hints and tips to design and conduct trainings.