Readme should state ,

• use in images either personal or commercial
• distribution , either individually or used ina bundle
• derivitive works (i.e this model or parts thereof may not be used to create other models for commercial sale )

Since most conditions rely on the honesty of the person using it , its largly a waste of time , unless you are lucky enough to catch them at it . Ebay regularly has people selling freestuff bundles but claim the cost is for the time taken to collect them .