We've never (yet) had a model look at their pics and decide they don't want to do more work, but I can see it happening if the model is iffy to begin with. On the contrary, while some of our models look at the pics and are like "Wow, it's really weird to see pics of myself nude" initially, most of them are actually really excited and delighted.

When I told our model Jesse that the Allboy with him on the cover was out, he didn't even wait for us to send him a copy... he rushed out to 3 adult stores in Toronto to find a copy, and was delighted to buy it (as was the owner of the store to be talking to the model in Allboy)

We do usually watermark the pics we give the models, and make it clear that they can't be used commercially or sold, but so far, we've never had a problem with a model misusing our pics.