Currently, in TurboActivate 3.x, verified trials are only possible using product keys, and you are in charge of deciding whether the customer is a new customer or no.
With TurboActivate 4.0 coming out in about a month, verified trials will be much better. You won't have to decide whether the customer is a new customer or not -- it will all be handled internally from within LimeLM & TurboActivate.