Some RMA equipment can just be a case of mistakenly purchased, you still have to get an RMA (returned merchadise authorisation I think) number so that the seller will accept it back and it can be dealt with quickly on return (they already have the RMA information on file and can send it for repairs, replacement etc as soon as they receive it). The dodgier side of RMA is when units are repaired and then sold as new without proper warning that they are repaired units. This is when people get screwed for full price on second hand or refurbed units because people don't know what they are getting.
Price wise it's a lot to do with the units only having certain hardware installed and the base prices are for basic hardware and no software. You have to supply a lot of bits yourself on the basic price
