I've bought a couple of patterns on Etsy from gals who had figured out how to do a couple of things I was struggling with. Their price, I thought, was reasonable, and they saved me a truckload of time. I also like Etsy when I'm looking for something unusual. I appreciate the handcrafted element.
I've purchased on Craigslist with great success and no shipping or delivery or tax charges is a huge plus.
I also like Ebay, I have purchased tons of stuff and never had a problem. I always have a price cap on things that I buy though because you have to include shipping, which can be outrageous!