Sorry, but you can’t quite compare Fiverr sellers to supermarket employees.
Fiverr sellers aren’t employees at all, they are freelancers who make use of Fiverr as a platform which connects buyers and sellers and acts as kind of an escrow service between buyer and seller, keeping the money the buyer pays until the seller delivered, and even beyond that, to give buyers a generous amount of time to check the deliverables. Fiverr doesn’t pay sellers a salary or social benefits or anything, sellers are free in what they offer, how they work, when they work, etc. (within the terms of service, obviously, they aren’t allowed to offer any services that are against laws, Fiverr’s and third party terms, and so on).
Anyway, if you check Fiverr’s terms of service, which all users, sellers and buyers alike, accept when registering their account, you’ll see that Fiverr excludes any liability for sellers’ acts or omissions unless it’s a liability which cannot be excluded under applicable law.
If the seller indeed did what you think he did, that’s certainly against some law or other but not in Fiverr’s responsibility (unless, perhaps, the seller did this kind of thing before and Fiverr knew of it and still let him stay on their platform, in which case they might be hold liable, I could imagine but don’t know the “applicable law”), you could try to sue the seller for compensation but that might very well only waste more time and money.
That said, this does indeed sound like a pretty unpleasant experience, and losing time with unpleasant things (and perhaps sales), of course, is always irksome. I’d see if I could prove to Fiverr that the seller did what you assume they did, so they won’t get another chance, at least here, to do it to someone else, and then leave it in their hands and spend my energy and thoughts on making your shop awesome
If you want to try with a seller here again, maybe make sure to choose one with lots of great and detailed reviews and who is on Fiverr since long enough that it’s improbable and would be very stupid for them to risk their account with an action like that.
Not saying that brand new sellers can’t be trusted, of course - we were all brand new once and glad that some buyers trusted us enough to buy from us without much or any “social proof” - but to “mend” your last really bad experience with some degree of certainty. Your shop and you certainly deserve a great freelancer to work with, and you should take your time to find one, especially if you’d need them for the long run, and I’m sure you can. Good luck with getting your shop functional and life ASAP!