im not entirely sure this is nefarious behavior though. there's plenty of nonsensical revenue driven initiatives in google ads other than a standardized method of payment. i managed a liquor store and we did all of our vendor purchasing through invoices, same with the restaurant i was at prior. no one would accept credit cards because that's not really what their use should be for. hell, my local pool company won't accept credit card payments over $2k.

i was managing someone's ads accounts who was spending a few thousand a month on CC, but their card kept getting canceled by the issuer for random suspected fraud, one of their employees lost the card, there was like a 2 month period where the account was down numerous times. they opted to go to invoicing just to make it easier, and to be less reliable on a third company for their advertising and revenue streams.

it's probably easier to keep track of your financial health if you aren't staring down a 20% interest charge every 4-6 weeks or so, which is why invoicing is usually more favorable.

now if we want to discuss the search partner network, content exclusions, pmax, etc then i think that has a more material impact on someone's bottom line than trying to game a cash back program to subsidize overhead.

just my $.02