Well, as I cannot afford much being a poor student and all and mainly buy good condition preowned stuff (Note: Make friends with your shop of choice. Mine are quite happy to let me choose the disc, manual and case that I want as they know that I pay for about half of their wages and bonuses).
However, I can tell you this. Companies seal new games in the UK on a case by case basis. Many first party titles by Nintendo are sealed, for example. However, the majority of Sony titles are not. Sometimes, Xbox games have a seal across the opening end of the case. Also, it is much easier to establish if it is new by going to their retail stores and asking(not possible if out of the country or ordering online, I know). But we are seeing a major change where many games these days are not sealed at all. Fortunately, the guys at my local gamestation know I don't take any crap and so wouldn't even try and con me.
Also, Zavvi (before they closed) mainly had display cases and all manuals, disks, cartridges etc. were kept in draws behind the tills. The amount of times they left grubby finger marks on the back of disks almost made me want to cry. But anyway, their DVDs were always cheap, and usually sealed.
