Retail Price refers to the price you can expect to pay at a brick and mortar jewelry store.
Online Price refers to the price you can expect to pay at an online retailer such as bluenile.com or others.
Craigslist refers to private parties (people not businesses) that are buying or selling a diamond.
Diamond Buyer refers to a business that buys diamonds from consumers.
Wholesale price refers to the price a 'cutter' would charge a jeweler or other retailer such as Costco.