One of the biggest decisions small business owners make when launching an ecommerce site is deciding on which shopping cart to offer. Long gone are the days when a PayPal button on your website was sufficient. If you plan to run a modern online storefront that’s appealing to customers, a shopping cart is a must.

Related: Shopping Cart Throw-down: Which Ecommerce Platform Reigns Supreme?

But, here’s where things can get a bit tricky. You’ll be choosing between a hosted (Saas) cart and an un-hosted (open source) cart. Pick the wrong shopping cart, and you could be stuck with a shopping nightmare.

Hosted carts, like the perennially popular Shopify, offer some ease-of-use benefits, especially if you lack technical knowledge. But these shopping carts also come with a high price tag, including a charged percentage fee on transactions. Furthermore, you won't have direct access to the code to customize your payments. On the flip side, open source carts may be free to use, but they also require higher technical knowledge.

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You may even end up shelling out extra cash for a professional web developer to install and customize your cart. What's more, carts have to be PA-DSS-compliant (referring to the Payment Application Data Security Standard) to accept credit cards. Upgrades to maintain compliance aren’t automatic they way they are with hosted carts, so you may end up spending even more cash than expected.

Which shopping cart is right for your business? It all comes down to the features and functions you need. Here’s what to consider:

1. Customization.

How easy will it be to customize the cart for your website? Don’t assume that opting for self-hosted/open source carts will make the customization that much easier. Pinnacle Cart, for example, is an extremely popular self-hosted cart option. Unfortunately, due to the cart’s limited templates, you’ll need to hire a pro to design a custom one for you. If you’re a professional company and willing to invest in professional design, Pinnacle Cart will offer you full customization opportunities. But, for smaller companies, the cost may not be worth it.

nopCommerce is another great option for customization, on a smaller budget. A devoted following is already growing around this free, open source cart option. If you have some basic coding skills, you can follow free online tutorials -- like the fantastic options available on Arixe -- and fully customize the nopCommerce cart to meet your website's needs. Another great option for customization is Magento. The self-hosted open source cart will require you to do some basic HTML editing, but once that’s finished, you’ll have a full one-of-a-kind storefront.

Related: 5 Ways to Win Back an Abandoned Shopping Cart

2. PA-DSS compliance

PA-DSS compliance is a set of standards regulating credit card data security. For ecommerce vendors, the most important requirement here is that in order for your company to accept credit cards for online payments, your shopping cart itself must be PA-DSS compliant. Certification is not a cheap process, which is why many “free” shopping carts still lack it.

Using a non-certified shopping cart is not a good option either: It opens your business up to a host of liabilities: If your online store were hacked, for instance, and your customer's credit card data were stolen, you could be held liable for all the fraudulent charges. To address this problem, businesses have two options: Use a PA-DSS compliant shopping cart or switch to an off-site payment gateway like PayPal. If you want to stick with your custom cart, then it’s imperative that you select a shopping cart with PA-DSS certification. Not sure about the safety of a particular shopping cart or gateway? Check with PCI to ensure your cart's compliance.

3. Ease of use

The right online cart will streamline your relationship with customers. Shopping carts handle multiple payments, collect the tax, offer shipping options (and shipping estimates, before purchase) and ensure a seamless transaction process. A straightforward shopping experience delights the customer. And a happy customer is your best referral tool.

Case in point: The DropBox referral program turned the app viral and built a $10 billion empire! Sure, you may not be creating a referral program on that level, but you do want to delight your customers each and every time they visit your site. Before the cart goes live, test it yourself. Is it easy to make changes to merchandise in the cart? How many steps in the check-out process? Can you see shipping estimates as you go? What about special promotion offers -- can you customize these? Ease of use is essential for both you and the end customer.

Bottom line:

Once you have a shopping cart in place, you’ve got a wealth of customer and inventory data at your fingertips. What items are most frequently purchased together? What cross-selling or upselling opportunities should you consider? How frequently do customers re-visit your site?

Related: How Shopify Became the Go-To Ecommerce Platform for Startups

Remember: The battle for ecommerce success goes far beyond your first sale. It’s critical that you A/B test, collect information and build databases to accelerate future sales success.