On one given day there were over a dozen shots for people who were not my customers. I had a recent client have to fire and artist because when they looked at the files on his computer, over half were from outside clients and the time on the files was during working hours. I say do this at your own risk. I think that if these questions come up in the first interview it should wave a red flag. Don't let the portfolio fool you.
Many artists have their diploma from the local art school.
Some of these schools will take anyone and give them a diploma if they pay the tuition. Most of the art in these portfolios is done from class projects and not real jobs. You need to see real jobs. Yes, I know that when the art is done, the artist doesn't have it anymore, but a smart artists takes a slide or picture, or at least collects some shirt samples. Don't let the samples and portfolio trick you into thinking there is creativity.