I agree with what's said above: a billing processor can scrub harder, but not shave. If they shave and don't grant the member access, it woud probably lead to a chargeback which affects them, not just the merchant.
Again as said above, I think closeness to chargeback threshhold would be th enumebr one reason why scrub might be more/less on any given day. It doesn't even have to be because of your individual account, it could be because of the overall average (depending what type or account you have with the processor).
However there are also reasons why sites might make more sales on some days than others. Let's say for a paysite, they update the content sometimes on Wed, sometimes on Fri, sometimes on Mon. The day they add new content, maybe signups are higher that day.
Or say a better example with dating, Monday is almost always our highest signup day because that's the day we mail people who chose to only get matches sent once a week. This increases our traffic and signups that day.
There are many factors and in the end, I don't think billing processors shave or try to steal your money; the few bucks here and there, is not worth losing clients or potential clients over a bad reputation
