Look at the packaging in the image. Most OEM sell their products, especially ones as small as USB drives, in a package about 4" x 6 “ or 6" x 8". The edges are mechanically sealed shut. Yes- they use the packaging you need to open with scissors or even a knife. Some fakes are starting to come packaged like th is.
If the outside appears to be cardboard, with a bubble showing the drive and staples holding it shut, the drive has probably been repackaged- and is likely to have been tampered with.
If the outside is plastic, but opens via a hinge, with two small plastic indents to snap shut, it is likely to be another example of fake packaging.
If you see a picture of the back of the packaging, does it include a serial number? Kingston Technology Asia has set up a site where you can input information from the back of a package, and they will let you know if it is a genuine Kingston Product. Unfortunately, they only cover drives sold in the following countries: Australia, Bangladesh, China, Hong Kong, India, Indonesia, Japan, Korea, Malaysia, New Zealand, Pakistan, Philippines, Singapore, Sri Lanka, Taiwan, Thailand and Vietnam.