You are 110% correct in your skepticism. I am a firm believer in "show me" when it comes to these Chinese phones. The vendors will say ANYTHING (I repeat, ANYTHING) to make a sale. Just keep in mind that once it ships, you're pretty much on your own, so choose carefully and wisely. You are absolutely without question right to be cautious.
That said, I have seen for myself there are phones that do indeed support the 3G (aka WCDMA) 1900 Mhz band though that was not stated in the advertising. I strongly believe that's because most of the world does not use the 1900 band for data, and there are more of "them" (aka, other human beings on this planet) that "us" (as in, well, the US), so from a marketing standpoint I get that.
Here is how I track down the truth about phone bands:
1) See if you can find the phone manufacturer and ask them directly (NOT a reseller). Overall, I have gotten very straightforward answers from the real makers.
2) Check reputable vendor sites to see how the phone is listed. I personally have bought from Geek Buying, and have frequently visited Antelife. I also hear Deals Extreme is good, as is Merimobiles. Send those sites the same question. I usually ask, "Does this phone have WCDMA 850 AND 1900?" or something similar. As I've posted before, get the vendor to say it IN WRITING so that you can open a winnable dispute later on if needed.
3) If the above is not possible, request an actual screen shot from the Android system itself. I forget offhand the specific key sequence, but there is a way you can see what bands are active on a phone.
4) XDA Developers - yeah, if a phone exists, there is probably a thread about it, and these guys get REALLY technical. STRONGLY recommend poking around in there.
5) If you decide to proceed with purchase, ALWAYS ALWAYS ALWAYS use a payment method that protects you, such as PayPal, etc. I don't like using my direct credit card number with these vendors, and PayPal, for all its faults, does offer some sort of payment protection. Another option, as Paypal isn't always possible, is an escrow service, where money is not released to the vendor until you receive the goods AND the goods are satisfactory to you. Of course, investigate the escrow services to see who has high marks for security, business practices, and so forth.
Please note that, if you have to return an item, you most probably will need to pay out of pocket for that, so do keep this in mind. So far, I've only had to return one (1) phone - and it was due to a malfunction, not the incorrect bands. Yep, I paid $35 for SECURE mail with tracking (worth every penny for the peace of mind), and I got a full refund of the purchase price.
Oh, and regarding the THL phone model you ask about - there is a thread on XDA Developers (a LONG one) dealing with this model phone (see
here). Btw, I have never personally seen any late-model THL phones with 3G 1900 Mhz. Not that it can't be possible, just I haven't seen it.
Forgot to add
Link to THL