Hi Sarah and welcome to the forum,
Yes, that is the style of site Karen is referring to when she speaks about Turnkey. It's effectively a walk in store where you do nothing pretty much, it's set-up with products and ready to start selling.
One of the problems with this style of e-commerce platform is that you don't know where the products are coming from and i many cases they may well be coming from the company selling you the actual store and this is where you can find the problem. With this type of business model the company selling you the stocked store is making their money on the store charge, not on you selling products, so they are assured of making their money, but you get no such assurances at all.
Without doing market research on the products you have for sale, you have no way of knowing if you even have competitive prices, you have no way of knowing what size the market even is for these products. In essence what you are doing is putting all your trust into the company selling you the site, remembering that the company doesn't care if you sell your products or not because they are making their money of the price of the store they are charging you.
Just step back from that for a moment and ask yourself if that sounds like a good idea?
It's a very tempting lure for new sellers, hassle free, low to no effort required, great looking site and so on, but anyone who has worked in this business successfully will tell you that success doesn't come easy in this market, you have to work at it, you have to put the effort in, there simply is no easy path to success like these types of sites promise.
The only easy path is to waste your money on a site that gets you little to absolutely zero sales while having it's hands in your pocket stripping out cash. That in a nutshell is why we don't and never would recommend this type of platform.