If you are trying to sell a product or service on your website and allow the customer to complete the payment process then you have an ecommerce website. These types of websites should be designed with the customer in mind, making it easy to complete the purchase and make contact with the business should they have any queries. For a customer to pay for a product or service online then they need o be able to trust your company. Adding logos that apply such as the PayPal logo or Visa Secured Checkout, can help build up that trust.
You need to carefully think about the layout of your site, making your products or services easy to find, easy to compare and most importantly, easy to buy. If your website asks the customer for a lot of information during the process or to create an account, you may find that this puts some people off. Ideally give your customers the option to create an account or check out as a guest. If you want people to create an account then give them an advantage of doing so such as being able to track orders, create repeat orders quickly next time etc.