If you're selling things online - from toys to ties, courses to memberships, it's likely that you'll want to take payment for some or all of those purchases. For that, you'll usually need a 'payment provider' - such as your bank, or a 3rd party system like Worldpay or Paypal.
We've worked with a few commercial payment systems, and there are a few factors you need to take into consideration when choosing a provider.
If your volume is low to start with, it's worth choosing a system that offers a very low annual fee - but may add a bit more onto each payment. Worldpay offers such a system , and we've found them very reliable.
If your volume is high, you may be better off using your bank's proprietary system or another provider geared to high volume. HSBC offers a great system and we've integrated with them successfully in the past.
Paypal is a 'love it or loathe it' system which some of our customers have implemented. It stores your card details for future use, which can be a benefit, but it does mean remembering a paypal password when you want to use the same card again.
It's certainly worth researching the choices and asking your web developer if they're able to develop your website with a particular payment provider in mind.