Authenticating a painting?
 

My girlfriend found a really cheap painting she liked in a thrift shop. She called me before she bought it and asked if we needed a painting for our new apartment. She said, "It's signed Harland Young, look him up to see if he's famous." I looked him up on the internet and saw some paintings that were worth a lot of money. I told her to buy it immediately and go home.

How does one go about having a painting authenticated/appraised? I'd rather not just walk into some random gallery/shop and be offered fifty bucks for something worth more than that. Of course, I fully realize that the painting may be a copy/fraud/worthless piece of crap, but hopefully it's worth something.

Thanks!