The term grey charges is new to me, but the concept isn't: these are financial parasites that suck off your bank or credit card balance for as long as you don't notice them. Like living parasites, they succeed by staying small and not hurting you too much at a time, costing the average consumer less than $350 per year but banging the entire economy for about $14.3 billion in 2012.
Grey charges depend upon us not spending with intent. Some of us can't be bothered to look at our statements, but it's just as common to be afraid to look at our financial situation. Either of these extremes is the opposite of living a life of intent, because earning and spending are part of the intentional life.
For those who find visualization to be a powerful tool, I have used the mouth of a parasitic lamprey to be used when imagining grey charges. These are the free trials that turned into charges because cancelling turned out to be harder to do than signing up; the innocuous little subscriptions that you don't use anymore; the official-sounding charge you're too embarrassed to call about because you don't know what it was for in the first place. They exist to slowly suck you dry.
They are one reason living only with cash is powerful -- if someone wants you to pay them cash every month, you're going to ask what you're getting in return pretty darned quick. At the very least, grey charges are a good reason to make a simple promise to oneself: do not send off a credit card payment without looking at the statement.
Spending with intent starts with taking responsibility for one's financial decisions. Grey charges live in the shadowing realms of "I don't have time," "I'm scared," and "I'm ashamed." Casting the light of scrutiny upon them is usually enough to dispel them, with vigor.