How do you get honest feedback on a new store from real shoppers?

Run a small paid test, even 50 quid of traffic, and watch the add to cart rate and where people leave. Strangers spending their own money are about as honest as feedback gets. Pair that with the session recordings and you'll see exactly where it breaks.

Don't ask people what they think of it, they'll be polite. Give them a task instead: "find a gift under 40 and get to the payment page", then watch them do it without helping and ask them to talk out loud. Where they hesitate or backtrack is your feedback. Use people who don't know you, friends of friends at least. And install a free session recording tool like Microsoft Clarity so you can watch real visitors too. Five or six recordings of people dropping off at shipping costs tells you more than any survey.