Trust is an important facet of strong relationships, whether in your personal or professional life. Building trust in the training field means doing your best for your clients and learners and being up front with them. If you take an already-built program, for instance, make small tweaks, and then try to sell it to a client as a custom creation just for them, you are setting yourself up as untrustworthy. Sure, you made one sale, but that client is unlikely to hire you again.
Learners are unlike