Make sure you get all the "fine print" with the costco deal. Be sure to read the thread I started and talk to them about the fees listed in my post:
All Costco lists on their website is: Mail Order/Telephone Order 1.99% + $0.27/transaction. In the fine print at the bottom it says there is a $20 monthly minimum. Make sure you understand how a monthly minimum works, it means that you need to be above roughly $1250/month in Visa/MC sales to clear it. It also states that Rewards Cards process at a higher rate. So the question you really need to ask is what is their Non Qualified rate, which is not disclosed on their page. You might also want to check if they have an AVS fee (Address Verification). If they have one, you can add an extra $.05 to $0.10 to every transaction. Also, check how much they are selling their equipment for.
You could a do a pre-authorization for the amount of your fees. Then close out the transaction when you deliver the service.
You would want a written agreement that you are authorized to charge a fee when they are a no show.