Here's my take on the issue, although I don't have any firm evidence.
I don't think there is actually mistrust with PayPal, but instead confusion as to how PayPal works. Most people don't want to give their credit card number to a company for them to store (although they don't realize this is partially what you're doing with any other company). People may think that setting up an account on PayPal gives your company access to charge them at any time. So instead they just want to enter their credit card and billing info without having it stored by PayPal. The problem here is that most people won't see the credit card and billing fields when they arrive at PayPal (for a number of reasons) so they have to instead click the small continue link to pay without a PayPal account.
I also think the second half of the issue is that people are going to a different site, which can be confusing. With most integrated solutions, they will never know unless they watch their address bar closely that they went to a different site as you can customize the payment page or you actually take the credit card on your site.
Lastly, I think it's just a general problem, if you want to call it a problem: People create thousands of carts every day to check what things will cost. For me in the past, the biggest reason for doing this has been to find out shipping costs. Many companies have so many options and such a complicated calculation to figure out shipping rates, that it's impossible for a customer to figure it out without creating a cart and then abandoning it. Having said this, you may want to look at other reasons why people are abandoning carts, such as:
- shipping rates
- tax calculations (maybe wrong or people aren't where you are so they don't want to pay your tax)
- prices for your products (are they dramatically different than other similar products, either higher or lower)
- number of steps it takes to complete the process (try to keep it to as few as possible, at least in my experience this increases sales)
- is the cart complicated or confusing (ask those without computer/internet/online shipping experience)
I personally like giving multiple payment options with PayPal being one of them. There are those that really like PayPal and don't like the idea of entering their credit card many times or just want to pay with through the bank account.