amex will deduct the rewards posted (and their actul policy is to post reward points only after u pay the next months bill which means 3 months since the original purchase this usaually protects them from shtik like this)
as mentioned above it most definatly falls under genevas daas as if you would ask the store straight out they would throw you out in a heartbeat so much for your plan
ps their is no easy way to earn honest money this is part of the klolu to adam
if its easy money you can be sure theirs a “catch” to it excuse the pun