When purchasing a model with a Standard or and Editorial License and when working under a contract situation whereby you are acting as the employee of a client, you can allow them future use of the models. The things to keep in mind are, that does NOT mean that you can continue to use the models for other projects as well as your clients. If you are working as their employee, then the models belong to them and not to both of you.
Also, if your Client were to come back to TurboSquid at some later day not via you, the models will show up under your account and not theirs and could therefore cause some issues. We suggest in these cases that your Client sets up an account and purchases the models themselves to prevent problems down the road.
Products with Custom Licenses should be reviewed on a case by case basis.