Do not delete your free models just sell them at a price even 1 or 2 dollars is better then just giving it away. If you give it to someone that's ok but it should be a friend or someone who already bought one of your models or someone who contacted you personally and wants to see the quality of your models before he buys something from you.
The problem with just having the models for free out there is that only free loaders will look at them the serious buyers will not and then you will get the reputation of someone who is not serious about selling.
I made that mistake a long time ago and it really did not help my sales.