Timothy Casey: Security.
Neither I nor any vendor recommended by me handle, nor have access to any credit card details you provide PayPal in the event of your purchasing any of my or my recommended vendor's products. It is wise for a consumer to avoid vendors who do not refer all internet credit card transactions to well known third-party merchant provider because the vast majority of vendors on the internet are unknown to any given individual. Statistically there is always a certain percentage of "vendors" who are running credit card scams at any given time.
When you choose, for example, to purchase a product via a PayPal vendor, you leave the vendor's website and go to a secure website provided by PayPal. PayPal forward the vendor only the purchase confirmation and the order/shipping details immediately your credit card is authorized and the transaction is approved. Without a secure and well known third party merchant provider such as PayPal to handle your financial transaction , it is certain that one of the merchants you try, will take advantage of the credit card information they have obtained from you.
On a cost-savings note, it costs the average merchant more to process and authorize your credit card transaction, than it does to have a large, efficient, and systematic organization such as PayPal take on the transaction for a small fee - and the savings are ultimately passed on to you.