Load testing for ecommerce

Before the sale, not during it.

When should I run a load test before a sale?

Early enough to fix what it finds. A test the week before a peak leaves time to act; a test the night before mostly tells you what is about to happen.

Can I load test checkout without placing real orders?

Test against a staging environment with the same shape as production. That is the usual approach, and it avoids polluting inventory and payment records.

What breaks first under load on a store?

Commonly the database and the session layer, because both are shared across every shopper. Testing tells you which, and guessing does not.

Does page speed really affect sales?

Speed affects whether people wait, and Google assesses Core Web Vitals from real-user data. Rather than argue the general case, measure your own pages and watch what changes when they get faster.