I guess one recurring problem is mis-description.
Sometimes it's quite deliberate - there's a blatant spec war (e.g. battery capacity, magnification of lenses, light output of torches, etc.) - then it pays to figure out what a sensible rating is for the item, and avoid anything which has an implausibly high rating. The sellers rely on the average customer never testing the rating. Sometimes even the quantity supplied is wrongly described, which is not too hard to spot...
Sometimes it is just bad translation - e.g. I was looking for an air duster to blow dust off. Lots of things described as dusters or even blowers actually suck rather than blow. I suspect there is no deliberate attempt to mislead here, just poor grasp of English, copying other people's descriptions, etc. Again, check carefully what you are getting (e.g. use Google image search etc to find the item for sale elsewhere, see if a better description is given).
The other thing, as others have said, is be realistic with quality expected vis-a-vis the price - it may be somewhat lower than the EU or US, but you are not going to get e.g. precision manufactured tools at pound shop prices. The advantage is greatest for light, low cost items that are very cheap to post, and in the UK, if the total is under £18, attract no import duty.
So, with the usual buyer beware, and making sure you know what to expect, I've been generally satisfied. When things did not work out (failed to arrive, arrive broken because of poor packaging, or not up to spec), either the seller has fixed things up or refunded me, or in extremis, AliExpress has given me a refund.
The main downside is having to wait up to a couple of months (and longer with covid) for delivery.