A client once told us their checkout looked cheap and asked us to make it prettier. We opened it, and honestly the design was fine. The problem was the seam: clicking Pay moved the customer to a page on a different domain, the logo arrived a beat after everything else, and the font wasn't the one used on the rest of the site. For about two seconds it felt like you had been handed off to a stranger to type your card number into.
We changed almost nothing visual. The payment page moved under their own domain, the branding got served with the page instead of loading after it, and the error messages got rewritten in the shop's voice rather than the payment provider's: "that card was declined by your bank, try another one" instead of a code and a shrug.
Now we walk the handoff points before anyone discusses fonts or spacing. Where does the customer leave your site, even briefly? What loads last, and who wrote the words that appear when something goes wrong? Those three moments do more damage to how expensive a site feels than any design choice, because they're the moments when money is on the line and the polish drops.
Somewhere on your site a customer gets handed over to something that isn't yours, and that spot is probably worth walking through yourself.