Who it applies to
The law covers a list of products and services, and e-commerce is on it. If you sell goods or services online to consumers, you are in scope, even if your business is small and even if you only sell within Spain.
The micro-enterprise exemption for service providers exists, but it is narrower than people assume and is measured on headcount and turnover. Two things matter: the exemption does not apply equally to every part of the law, and on the day a customer complains, nobody will accept "I thought I was exempt" as an answer. If you are near the threshold it is worth complying anyway — it costs little to do properly from the start and a great deal to retrofit.
The eight fixes that carry the most weight
A full WCAG 2.1 AA audit runs to dozens of criteria, but in a normal shop most real failures cluster in a handful of places. These eight cover most of what gets found.
None of them is expensive if the shop is well built. All of them are expensive if the template has to be rebuilt, which is exactly why it is worth asking before commissioning one.
How to check without paying for an audit
There are three tests you can run this afternoon that catch most of the serious problems. First: complete an entire purchase using only the keyboard and the tab key. If you get stuck anywhere, that is a failure that blocks some of your customers completely.
Second: set the browser to 200% zoom and see whether buying is still possible. Third: run an automated tool over the product page and the checkout. Automated tools find roughly a third of the problems, which is not enough to certify anything, but is enough to tell you whether you have a large one.
What a tool cannot see is whether your alternative text describes something useful or says "image1.jpg". That needs a person.
What you gain besides compliance
An accessible shop is an easier shop for everybody, and that shows up in the numbers before it shows up in a compliance folder. Enough contrast helps anyone shopping on a phone in direct sunlight. Clearly labelled forms get filled in with fewer mistakes. Explained error messages reduce carts abandoned at the payment step, which is the expensive step.
And there is a side effect that rarely gets mentioned: almost everything that makes a page accessible — sensible headings, alternative text, clear structure — is also what helps a search engine understand it.