1. reputation (esp. when someone on the board speaks highly of or recommends one of their notions)
2. ease of navigation through site and variety of items
3. cost including free shipping
4. if the site offers other things... I am likely to navigate to that site and stumble upon something I want (ex: Leah Day has great tutorials on FMQ; after I check out the info, I end up buying something.)
5. Samples of completed projects using the notion or tutorials on how to use it help.