Cash money is always preferred. But they're both money, so yeah, we'll do either.
But (insert credit card company name here)'s fee is going to be roughly 2.8%. That fee essentially comes from our pocket, if we're trying to keep our prices low. We may give some kind of discount for cash purchases that are of more than marginal amounts. If you're buying a $5 item, I wouldn't expect much, but if you get 2 kits, a carboy, a thermometer and some caps -- well yeah, we'll probably consider it IF YOU ASK. You don't ask, we won't offer ; ) It doesn't seem like much until you add up the CC fee column on the year-end spreadsheet. We've all been practically brainwashed in the name of convenience and "security!"
It's a similar philosophy on our kits -- we include priming sugar and yeast, but if someone already has those items from a prior brew session or in bulk, I'd rather save them for someone else than give it to you if you don't need / want it. Most poeple are not particularly stingy (though there's really nothing wrong with that - they paid for it!) and are cool with that.
We're a super-small new shop and it helps us to keep prices at a reasonably low level as well as it gives us the ability to offer the occasional incentive to our "regulars."
Cheers!