Our experiences are similiar to GS_Dirtboy and others.
Most recently, we arrived at EZE in October with a very nice used mt. bike and lots of mtb gear. It was all well packed in a discrete looking cardura type bike bag and I intentionally left it dirty as well. Most importantly, accessing it for anyone who may have wanted to would have been cumbersome and slow. I bubblewrapped and then used the brown packing tape you would use to secure a cardboard box to protect the frame and components. I actually photocopied the receipt and left a copy directly under the opening of the bag (probably not needed) so that if someone looked inside they would see it first (two years old). We went right through the scanners without issue... same experience (knock on wood) over countless trips with skis, snowboards, climbing gear... Our advice- if the items are new(er)- go take them for a trip or two in their intended enviro and then leave them as they, just pack 'em up that way- but it's hard to say with total certainty- good luck.