An online store has to win people over with nobody there in person. Whoever comes in wants to know in a moment whether you have what they are looking for, whether they can trust you and how much it will cost to get it delivered, and if it does not look clear, they buy somewhere else.
Opening is only the beginning. You need product pages that Google understands, a cart with no surprises, the languages and the shipping zones, the emails that bring people back and, if you come from another platform, a switch that does not cost you your customers or your place in search engines.