If you are talking smaller quantities, I must say I've had good experience selecting sources via Alibaba.
In the end, it's down to trust. If you want samples, then the cost of these is fractionally higher - just be aware of the minimum order quantity. This always causes me problems because I perhaps want a stock of 10-20 per item, of perhaps 20 different items, and they want me to buy 50 as a MOQ - so some slow lines that are good products I have to forget because I can't afford to tie too much up in stock.
Delivery, despite any promises is slow. 3 weeks ago, 3 day delivery time items will be arriving via air freight sometime soon - it's rather like dealing with Spain and Italy - 'soon' is a very elastic term. Price quoted are often very high for freight - sometimes, in my case, nearly as much as the actual goods. Remember that if they come air freight then they will probably be delivered to you in the UK by carrier - who will then invoice you later for any import duty and VAT charged. Sometimes there is no duty, other times there is. The HMRC site is not good at categoric yes/no decisions - much relies on the interpretation by individual officers on the kind of items I deal in (which is microphones).
With electronic banking, the old letter of credit system isn't required, you can pay the funds into their account as you would a UK supplier - BUT - one thing to watch. Many of the firms have a single bank account that services a number of beneficiaries, so sometimes you get emails asking where the money is, despite your own bank reporting the transaction complete. Eventually they find it - I've not lost one yet, but it frequently takes them 2 weeks to find the funds!
Your samples may well be made by hand, and perhaps not made till your funds have paid for the raw materials, so sample time is quite long. They frequently advertise things that are not in stock. They make them to order. Their packing is not as good as ours for delicate items - they're pretty much like we were twenty years ago - lots of cardboard, not a lot of bubble wrap for delicate items.
From time to time, manufacturing standards slip. With my microphones, the performance is fine, but the cases perhaps have the occasional burr, or sharp edge that quality control didn't think important.
The last thing is that emails can be tricky - they have business English, not social English, so they can appear rude and pushy - but they're not really - in fact they are very keen to do repeat business.
I have had one single problem item, and that was really down to the carriers thumping it around in flimsy packing. I'm really pleased with the business I'm doing, but you just have to realise they have their own way of doing things and you cannot change this.
I suspect the Alibaba network generates them a lot of trade, so like ebay, negative comments are not wanted - so they do try.
For my kinds of quantities, I can't justify going out there - but when you reorder, they do remember you - even if you were a small customer.
Paul