This is why I'm a software engineer and not a retail tycoon ;-).
For example Mercado Libre. Originally from Argentina (I think) but it's all over Latin America now. They used to have auctions but at least in Mexico it's mostly a marketplace.
Maybe I'm just extremely cynical, but you don't feel those are somehow gamed? For parts that you've described, I've actually moved to eBay as my first stop.
I think the reviews for products are gamed but I don't think the seller feedback ratings are.
I used to sell used books as a Amazon marketplace seller and I once sold a book that was damaged and put that condition in the description. The buyer bought and gave me 1 star rating for it and described the damage that I already put in the description. The buyer just didn't bother to read the description before he bought it. I couldn't get Amazon to remove that unfair rating.
If there's a way to game the seller feedback in a sustainable way across thousands of ratings, I'd like to know how. Sure, sellers could offer refunds to bribe customers to change their seller rating from 1 star to 5 stars (not sure if that's even possible) but eventually, the seller will run out of money with that scheme. On the other hand, product reviews are easier to hack.
But for many things I shop for, that would be extremely inconvenient for me. For example, I needed to buy replacement fuses for a Fluke multimeter. Amazon itself didn't sell it but a 3rd-party marketplace seller did. If the marketplace was shut down, I'd have to go through the hassle of registering a new account on yet another ecommerce website just to buy that fuse. In this day and age of customer databases getting hacked, I'd rather not create any new accounts unless absolutely necessary.
Yes, I get the danger of counterfeit items. I did get bit by that with fake eclipse glasses from China last year but nevertheless, the 3rd-party marketplace has been a net positive for my shopping experience. I just pay attention to the seller ratings and make sure they're better than 98%.