As Johnny D says, likely damage from storage or due to careless handling. An aluminum rim is much softer than many building materials like stone or bricks or steel, so it is possible that the rim got dropped or placed somewhere and that caused the little damaged spots.
(a) There is 100% no problem with riding that rim...
(b)...but it should not have been sold as 'new' at full price, but rather as a 'scratch'n'dent' or blemished item with some percentage off MSRP. But if this rim is going on a bike meant for riding and not just for looking at, then just build it up and ride - such scratches are very common from regular riding. If I went to the LBS to buy a rim this afternoon I would expect to have that amount of damage by the time I got home just from the rim being in the trunk of my car. I might notice the damage as I laced the wheel, but it wouldn't stop me for one second from riding with it.