It's the latter — on aliexpress or tradetang or taobao you could just add it to your cart, checkout, and pay with no haggling. Shipping is often free, as EMS and Hong Kong Post have normally very low rates. On DealExtreme and many eBay stores you can order a 99¢ item with free airmail from HK and get it a few days later.

On Alibaba, you have to talk with the seller for anything to happen. Though some of them work directly for a factory, many of the sellers are total freelance agents, and even the ones that work for a factory will act as agents to resell items from other factories. You can usually suss out how direct a seller's relationship with the ultimate supplier is, and they'll often tell you outright, though none of them seem to be willing to talk about each other. All of the ones I've interacted with have been ~30yo women that seem to be working solo as agents with other people doing the fulfillment.

The other thing is that they very rarely put up enough information to find out what the product actually is. Often the product can easily be made-to-order with finishing options up to you (though the factory does all the product development). You end up looking at a bunch of agents and looking at pictures, weights, and options to discern who's reselling what. Occasionally the OEMs will have product data on their websites and you can backtrack from there. It's kind of maddening but none of them really give a shit.

Even if you think you know what you're getting, you still want to get spec sheets from them for confirmation, and spreadsheet catalogs of similar stuff so you know you aren't missing anything (they don't keep their listings up to date). Even after that you still have to go back and forth on quantities, prices, shipping, lead times, options, potential setup fees for customizations, etc. They do like MSN and pasting stuff into excel documents to send via direct file transfer. It works ok once you get that far, but it feels really sketchy.