1. Credit When Credit is Due Taking Credit Card Payments in Evergreen
Dawn Dale

2. PCI-DSS Payment Card Industry – Data Security Standards
API Application Program Interface
GUI Graphical User Interface
Payment Gateway A merchant service provided by an e-commerce application service provider that authorizes credit card or direct payments processing for e-businesses, online retailers, bricks and clicks, or traditional brick and mortar. Examples available at:

4. Stripe is an open source software.

5. Standard Transaction Fees
PayPal Payments Pro
No startup costs, no termination fee
$30 monthly fee
You provide customers with a fully customized checkout experience right on your site
Includes Virtual Terminal to allow you to accept payments over the phone
Standard Transaction Fees
These fees apply when you sell goods or services online (including using PayPal Payments Standard and Express Checkout) and in your store location and the buyer pays using his/her PayPal account.
No startup costs, no termination fee, no monthly fees
Accept PayPal payments with Express Checkout
Accept PayPal payments and all major credit cards with PayPal Payments Standard

6. Standard transaction fees for charitable organizations
Discounted credit card processing fees for registered charities with 501(c)(3) status. Learn more about our discounts for charities.
If you’re a verified charitable 501(c)(3) organization,
and the funds you are receiving are coming from a PayPal account: then you pay:
In the U.S. a fee of 2.2% of the transaction amount plus a fixed fee based on the currency.
Outside the U.S. a fee of 3.7% of the transaction amount plus a fixed fee based on the currency.

7. Micropayment Fees
If your transactions are less than $10, you can save money with our micropayment processing fees.
If you qualify to receive micropayments pricing and the funds you are receiving are coming from a PayPal account in: then you pay:
The U.S. a fee of 5.0% of the transaction amount plus a fixed fee based on the currency.
Outside the U.S. a fee of 6.5% of the transaction amount plus a fixed fee based on the currency.

8. Payflow is strictly a payment gateway and nothing more.
If you want to use this services you need to have your own processor in mind. In other words, this service alone, doesn't process credit card charges or make them. It only "formats data" to be sent to processors.
I quoted formats data because I'm quoting what the specialist said to me. I don't exactly know what format and how, but what was made clear to me, is that neither Payflow nor Payflow Pro does the job of  charging any cards.
So in, short, this service alone cannot be used in place of Stripe. It can be used in tandem with a processor to achieve the same objective, but you'll need to mind the costs.
I should also add that I was looking for information about this service so I could use it for a Canadian based e-commerce solution. Perhaps the US based version of the product might differ.

9. Accepting Payments via the OPAC
(For Your Library)
Accepting Payments via the OPAC
Vendors / Pricing
Vendor
Setup Fee
Monthly Fee
Transaction Fee
Notes
PayPal: Standard Pricing
2.2% + $.30 per transaction
PayPal: Micro Pricing
5.0% + $.05 per transaction
$13.00 breaking point 
Website Payment Pro API
$30.00 
n/a
Credit Processor necessary for using PayPal
Stripe
2.9% + $.30 per transaction
Authorize.net: Standard
$49.00 
$25.00 
Authorize.net: Simplified
Less than $ per month

10. Library Settings Editor