Not trying to be a douche, but a scraped up floor plate isn't really that bad. A file and some hi-temp rattle can paint and a little elbow grease and that mag can look much better in 10 minutes or less. It would cost me more time and effort to even try and return it. Remember we are buying surplus - as long as the mag is functional, I'd say keep it and chalk it up as a lesson in life on subjectivity in conditions. I usually buy 10 or more at a time assuming at least one bad one in the group which can be used as parts when I get another bad mag through another purchase. If you want new, buy new....but the risk with buying surplus in bulk far out weighs the cost of new mags. Please keep in mind the cost of the mag, as they were a great deal. No need to bash a good vendor. Sam is a stand up guy, and I know you are upset (I've been in your shoes with another vendor), but that's the risk of buying surplus.
If I were you, I would use this as a great opportunity to try and restore a mag. It's not that hard if you have some spare time. There are threads on here on ways to do it. You can easily make that mag look brand new from 5 feet away in short order with tools/supplies you should already have around the house.
Good luck!
Seriously - give it a try.