After receiving so much invaluable information from this thread it is now my time to give back.

In the last three weeks I have entered China with an Austrian passport via Chengdu Tianfu (inbound from Istanbul), Tianjin (left via PEK), Shanghai Pudong, Xiamen and last but not least Guangzhou. Transit through PKX.

In Chengdu I went straight to the 24h/144h desk, because I planned to stay for 30 hours....only to be informed that in Chengdu that is not necessary as they handle TWOV until midnight the following day solely via Temporary Entry Permit stamp and no TWOV sticker like all the others do.

In Tianjin I have been accompanied by young state security agents from the Tianjin Airlines flight inbound from KIX (they escorted me out of the aircraft before all the others, incl. Biz were allowed to disembark). to immigration and customs. I was the only non Japanese, Chinese on board.... Despite only planning to stay a little bit less than 24 hours in the TSN/PEK I received the 144h sticker.

Shanghai Pudong was straight forward 24h sticker for a 17h overnight layover.

Xiamen has been by far the most relaxed, despite me making the mistake of forgetting to include the flight number of the outbound flight the following day in the screenshot of the confirmed flight reservation. They need to fill in the flight number, so they looked it up in their system themselves.

In stark contrast the two guys at the Temporary Entry Permit - 24h/144h counter at Guangzhou Airport have been by far the strictest. They had an issue with the Istanbul stamp, until I explained to them that it was only transit on the way to Chengdu. The two Turkey stamps had the same date and the Chengdu TEP stamp the date of the following day. They also questioned the previous 24h TWOV stamps (why only so short....) etc. From what I have seen while waiting in line especially UK citizens have been asked a lot more in-depth questions, compared to the others....but that was only in CAN.

Out of all the Airports I arrived in China all the other Enquiry desk employees literally bent over backwards and went above and beyond/the extra mile in helping and supporting me, calling the Airport Hotel to organise the pick-up etc., but not so in CAN. Officially they have no phone....but they want to sell you a Sim card for 180 RMB.

In PKX I have only had a four transit from Xiamen Airlines inbound from DOH to China Southern outbound to Seoul Incheon.

If one has checked luggage at PKX the Airline sends someone to pick it up from the luggage belt and completes the recheck-in. No need to go through immigration/customs.