I can think of two reasons:
1) True cost of transaction. Assuming you are using a foreign credit card, you will get hit with a % surcharge, plus DCC (dynamic currency conversion). This can raise the actual cost, once the transaction is processed, of an additional 5-10%.
2) Recourse in case something goes really awry. You'll be under the laws of the PRC, which aren't particularly customer-favorable. This is even more important now that ctrip has changed its business to an open platform from which hundreds (thousands?) of agencies can use to attract clients. While one can chargeback against foreign credit cards issued under the laws of many developed countries, there is still a cost for disruption of your plans, especially when it happens in real time.

As for the example given by @moondog above, I flatly find it hard to believe that ctrip has that big a differential in ticket price, without something being very very amiss. There's got to be a catch somewhere. If it's too good to be true, it probably isn't. A cautionary tale being the ctrip ticketing scam earlier this year, which I think we referenced on another thread here. If what ctrip is offering is a completely legitimate deal, then you can bet that other OTA's will have the same deal, even if the airlines themselves don't. And seriously, a fairer comparison by moondog would have compared ctrip's price to other OTA prices for the exact same ticket, same dates. The airline.com sites are generally always going to show higher for premium fares so limited the ctrip comparison to those is hardly an accurate apples to apples comparison.

Believe it JieJie. I've used these fares for the past 2 years. Nothing has ever gone wrong for me on the Ctrip side of things. I can usually get AA PVG-LAX or SFO round trip in biz class for 2200-2500 USD. Sometimes it's even cheaper. The one time I had a problem is when AA delayed the flight by 10 hours due to "crew rest issues". Ctrip promptly refunded the entire ticket amount to my Union Pay card and I purchased another ticket on Cathay.

For the specific HKG-LAX fare the dog mentioned, they have been offering this since mid-August leading up to the launch of the flight. The only online travel agent I've seen it on is Ctrip. It doesn't show up on Kayak or any of the other sites so it seems to be an exclusive deal and someone who wants a business class flight on that route would be nuts to pass it up.

Ctrip customer service is far and away better than any of the USA online travel agencies and I would have no hesitation about using them to purchase tickets anywhere in the world and have done so numerous times!

But you are not addressing my main concern. You are talking about flights originating in PVG or HKG. I specifically mentioned/implied in a post above that for intl flights originating in China (I'll extend that to HK) ctrip is not a problem and I have used them for these sorts of flights. But @no1cub17 was talking about a USA-Europe flight, and I see a difference in that. I find it very hard to believe that ctrip would have some sort of special insight on this sort of routing, that momondo or some of the other OTA's would not have.
I have increasing doubts about ctrip, so I'm happy that your experience with them has been hunky-dory to date, and that you have a rousing endorsement to use them for any ticket from any two points. At this point though, I personally prefer to limit my exposure for any one ticket/transaction with them to under USD 700-800.

The reason this sidebar exists is because Ctrip IS offering exclusive fares in markets like US-Europe.

Exactly. Especially for one way fares to Europe, ctrip is far cheaper than any US-based OTAs, much less the airlines (which only sell full-fares to Europe). Yes, similar fares exist via momondo through exploretrip.com, but they have even worse reviews than ctrip.

If I really should not buy a ticket on ctrip (that doesn't start or end in China), please let me know why.

There is no reason you shouldn't buy this ticket. I've bought many tickets via Ctrip for flights that don't go anywhere near China, never had a problem. If they have the best offer, use them.

We're not going to change each other's minds. my gut says ctrip is going skanky and quickly, like so many Chinese companies tend to do. I question HOW they are able to put out these drastic "exclusive fares" when nobody else in the marketplace seems able to do so. If there's no gotcha for the consumer, then either they are shaving profit to nothing or putting out some loss leaders and having those losses covered by....well, let's say I have my suspicions over how they're able to make this pencil at least in the short term. I don't particularly trust ctrip as much as I used to, and while I will use them selectively (primarily in the China domestic and ex-China intraAsia routes), I will also limit my total ticketing exposure amount at any given time. You all do what you want--there's no point in continuing to argue about this.

Following is my hypothesis:

1. When AA launched its China routes, they had zero brand recognition in China
2. Ctrip stepped in to drive demand, and did a good job
3. AA asked them for help on HKG-LAX
4. Since #3 has been successful, AA broadened the scope to include other markets

Whether or not the above is true, avoiding Ctrip because of DCC in the context of a 4-figure fare difference is kind of silly IMO.

Can you not get this fare on aa.com? I heard the same thing about business class fares ex-China on CA, HX and UA and while good, I can always get same or better directly from the airline website. Currently I am paying about 2000-2500 USD roundtrip in business to the US (even on UA) and I do not need to worry about avoiding Ctrip's insurance tack-ons and ridiculous "buy this fare with an obligatory hotel coupon upcharge"

I'd never use Ctrip outside of "Greater China" just like I don't trust Mainland Chinese airlines on longhaul routes. It's not about any prejudice but rather mirroring Chinese/Cantonese thoughts.

On the other hand, they are perfect for China - Korea RT flights in discounted biz class or the odd domestic Middle Kingdom flight if train connections are too cumbersome.

The lowest I've seen HKG-LAX on aa.com is $4500. The $2200 ctrip fare is available on all dates that I checked.

How does it work with these flights that say "ticket later"? They guarantee you'll have a ticket by 72 hours prior to flight departure? Is this reliable?

In my experience, this is >95% reliable, and confirmations typically hit within 24 hours of booking.

Thanks

Re: DCC. I just made a booking and during the payment step it gave me a clear choice if I wanted to pay in USD or CNY with exact exchange rates. ^