The present disclosure relates to systems, non-transitory computer-readable media, and methods for intelligently determining to assess (or not assess) a cancellation penalty and notifying a requestor device of such a penalty in response to either a requestor's selection to cancel a single transportation request for a requestor or a requestor's selection to cancel a shared-transportation request associated with multiple requestors. For example, the disclosed systems can generate conversion probabilities for a requestor reflecting if a cancellation penalty is assessed—and if the cancellation penalty is not assessed—for a cancellation of a transportation request for transport of a lone requestor. Based on the conversion probabilities, the disclosed systems customize a cancellation notice for a requestor device to either include or exclude the cancellation penalty. Additionally, or alternatively, in certain implementations, the disclosed systems generate a transportation efficiency metric for modifying a projected transportation route for a shared transportation to account for a cancellation of a shared-transportation request. Based on the transportation efficiency metric, the disclosed systems customize a cancellation notice for a requestor device to either include or exclude the cancellation penalty.