I tried offering free models when I first joined, but I'm completely over that now. Free models appear to have no impact whatsoever on sales; I'm guessing that people who download free stuff aren't the same sort willing to pay for a product. Unfortunately for me this is my job, so customers is what counts, and likes and rep and whatnot is only marginally useful that it may influence a potential customer to take the plunge on one of my items, but I doubt even that is true.
But the lack of any form of "thank you" or anything from downloaders really did get on my nerves. It just seemed rude for so many people to take my stuff without the most rudimentary acknowledgement.
And to add insult to injury, these free items will eventually show up as a "for sale" item either on this site or elsewhere; so not only has someone taken my free item, but decided to profit off my generosity. That for me was the final straw.