Best CMS For e-commerce & Web Based Services

I'm considering starting a new business that provides various seo and social media services. Wordpress is usually my go to CMS, but I don't believe it's my best option for a project on this scale. Can anyone suggest an e-commerce platform that offers great sales and order management for both myself and my customers?

For orders customers will select a service, provide me some basic information such as a URL, and a quantity for their order.

Customers should also be able to login and manage their accounts, orders, and get support if needed.

Is there anything like this out there written in PHP that won't require serious modifications to the source?

OPENCART & MAGENTO both are good.

well if u are only uploading limited number of products than wordpress woocommerce should be good for u.. else there are always custom scripts available.. google them
if u have like 100+ products go with magento or opencart

magento. Tried almost all of them.

Thanks a lot everyone, I'll take a good look at magento.