Alibaba and Aliexpress are very different kinds of services. Alibaba is wholesale and it consists of shitload of different suppliers/ factories. There is no way saying in generally that is some a scam or not. It depends.
The mentioned delivery date (to port) is usually about a month or so, but can be several months too + shipping from China to where ever you want the stuff to be.
Aliexpress is like local Amazon.
I don't know what you are ordering, but if you are ordering like 1000 pieces of something it won't hurt to ask several samples. Those samples are also usually better quality products than the actual products, so keep that in mind. The quality varies very much. If the factory owner's idiot cousin was in shift to make your products.. tough luck, if not, then kudos for you.
If you really want quality products, etc. you have to get local representative. There are shit loads of those too, just don't hire the factory owner's idiot cousin.
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