I think one thing to consider would be how long the store has been in business. But even that isn't a guarantee anymore...
If you're on Ravelry, there are a lot of free patterns there (you have to sign up for an account if you don't have one).
You can also take a look at www.knitty.com
And there are hundreds of free patterns at Knitting Central:
You might want to narrow it down to a few patterns you like, and then think about yarn weight, fiber content, etc.
Good luck, and keep us posted!