You cannot charge customers more money to pay for something using one method of payment over another. It also wouldn't be a very good sales tactic as the customer has most likely decided to work with you based on your current price and the fact you can offer finance. 

There is no fee to offer your customer 11.9% APR over 3-7 years and it suits most use cases. If you decide to offer 0% finance to all your customers then we recommend that you adjust your margins accordingly knowing you may incur more costs on these deals.