Future reference for buying used (as opposed to "sealed in box" or "like new"): before going to see the device, try to figure out how the hinge feels in an original SP. When you're there looking at the device, do a test of the hinge. The farther away it feels from "original", the more likely you have a refurbished/repaired or bootleg device.
As far as distinguishing the difference between repaired and original, you just need to have an eye for detail. Use the knockoff-identifying skills you learned from Redd in Animal Crossing as a kid. Bootlegs always have some sort of tell that identifies, visually, whether it's fake. Just be careful, as aftermarket shells can also carry the same tells as a bootleg console.