I am an enthusiastic user of RTS, and it appears I was the 7th account to sign up with Mercury Pay. I don't sweat the charges, because I approach them from the other end. I make what I want on my products, and things like credit card fees are added on (averaged overall).
3 or 4 years ago, I noticed that RTS was working with other companies. However, the charges notwithstanding, I've been very happy with Mercury Pay's service. I gave them a call and basically just asked if they were giving me the best rate they could. I ended the call, happy, and with a lower rate.
The forces driving credit handling seem to change. like anything else, but they certainly won't go down if you don't ask. Ever see how fast your personal credit card terms can change when you call and say you're going to cancel?