I work at an LCS dumb fuck.
Marvel on occasion will make match orders with Diamond. Say I order 100 copies of Avengers #3. Marvel might have a "deal" going where for every 50 copies ordered they add 25 more copies of Avengers #3. Giving me 150 copies of Avengers #3 total after ordering only 100.
Or sometimes it's another book like for every 100 copies of Avengers #3 I'm given 15 copies of Thor #5.
This pads numbers on units because to Diamond it looks like more copies of a book are being ordered. Avengers #3 effectively jumps up 50 units just because I ordered 100. But it doesn't effect the dollar unit because these added issues aren't being bought through them.
What's annoying about this practice is cost of shipping goes up for me because more product and weight is added than I ordered and I have to make room for extra copies of a book I may not have wanted.
However this practice can be anticipated meaning I do have an option to anticipate the extra issues given and factor them into my initial order.