Is that a Robot Kingdom purchase? They seem to have be left with boxes and boxes of unsold DOTM cards and are giving them away quite freely (just to be rid of them) if you buy anything - not Prime in particular.

Free TF Movie 3 Trading Cards for every orders and unsent Preorders!

For every USD50 ordered, 4 pack of TF Movie 3 Trading card will be included.

For over USD300 Order, A Card Album will also be included!

http://www.robotkingdom.com/news/item/index/id/117/