I'm pretty sure it wouldn't be hard to implement late fees, but passing your processing fees onto your customers is a different matter. First off, some states make it illegal to do so, so you wouldn't be able to directly pass those fees onto them if you live in one of those states. You would need to ask your state's taxing authority, or a good business lawyer, about the legality of doing this. If it's not legal, there are a few work-arounds you could use. Many people here have suggested simply increasing all of your prices by an amount that would cover your processing costs (typically 2.75%, although that can vary depending on the method that the charge is entered and which system you're using.) Then, at checkout you can offer cash/check/gift-card, etc paying customers a courtesy discount of about that same percentage so they don't pay for process costs that they're not causing.
Judy T Shumway
