Cart & Checkout interview questions

Cart persistence, checkout orchestration, tax and shipping, and conversion-critical failure handling.

3 questions in E-commerce & Retail.

E-commerce and RetailA 19-minute read on how the topic fits together, before the questions.E-commerce and retail fundamentals58 short answers on one page, for revising rather than studying.

medium1

mediumScenarioDesign

A shopper adds items on their phone while logged out, then signs in on a laptop where they already had a cart. What should happen?

You have two carts and no rule that is right for every case, so the merge has to be a deliberate product decision rather than whichever write lands last. Prices and stock have both moved since the older cart was created, which is the part that turns a session problem into a correctness one.

4 minmid, senior

hard2

hardDesign

Design the checkout flow for a marketplace with multiple sellers per order.

Persist the order in a pending state before you touch the payment gateway, quote tax and shipping per seller shipment, authorise once behind an idempotency key, and commit the remaining steps through a transactional outbox and a saga whose compensations void the authorisation and release reserved stock.

7 minmid, senior, staff

hardDesignScenario

Checkout calls pricing, tax, fraud, inventory and a session store. Which of those are you willing to carry on without, and what does the shopper see?

Sort each dependency by what the loss looks like. Price and payment authorisation must fail closed because the loss is unrecoverable; personalisation degrades silently. Tax and fraud sit between, and the answer is a written policy with a bounded exposure, not a timeout value.

6 minmid, senior, staff