If I buy a power tool, use it for a project, then return it, surely that's as open to abuse?
Games retailers should utilise the same tools as others - don't sell to people you think are abusing your return system.
Most retailers are pretty restrictive and those that aren't, such as REI, have generally been notable for those policies.
In my mind, software return policies should be more liberal than physical goods since there isn't any potential loss to the retailer due to damage.