I'm working on a sort of CMS with a built in payment system. We plan on having it support multiple payment processors like Paypal, Amazon, and Google Checkout, but I'm wondering if we need to present all of those options to end users or just have the person setting up the server pick one. Are there any studies of the effect of having multiple payment providers on conversion rates? Do buyers appreciate the flexibility of multiple payment options, or is it just one more thing to have to understand?
I work at an eCommerce website and adding PayPal (though buggy) helped out conversion rates. However, adding a bunch did not.
If you are building a CMS I believe it is best that you allow who ever is setting it up to choose which they want presented to users and to use. They might not want their money split up.
The answer is going to be fairly region specific. For example, if you were setting up PayPal for a site targeted at a country that doesn't have a high penetration of credit cards, you would likely not see much benefit, and you should look at more regional payment solutions.
Most people only care that their preferred method of payment is available, so you need to know who your audience is and what they prefer before you can know if it's worth doing or not. Ask a sample of your customers and see what they prefer using.
I remember reading a paper on e-commerce and payment methods a while back - i think it was from econsultancy. The outcome of which was that the options that should be offered varied greatly dependant upon the country the website operates and sells in.
In the UK credit cards are a very popular online payment method, however for example in Germany credit cards prove a far less popular payment method so ideally you need to ensure that you offer payment methods that allow customers to pay by whatever means they feel comfortable with or have at their disposal.
It is very much dependent on the people liable to use your sites. The expectations of the user are paramount - as @JohnGB points out, people only care that their preferred method is there - the end users do not want a choice, they only want the one option that they want to use.
Providing the clients with the ability to select - and select choices based on country or community - is probably the way to go. This means that choices can be made early on, and the end users are not being asked to make choices.
Sure, you have to allow users to choose. US-located users may prefer to use credit card, but non-US users may prefer to use PayPal as not all the countries have convenient credit card environment/services. Also note that pricing shouldn't vary from payment method to payment method (even if you have to pay some fee as a merchant if user select, for example, credit card as a payment option). You may read more about usability issues during checkout process here.