SADAO REPORT 27/07/17:
Got my 4th back-to-back SETV from Penang through Jim's Place no dramas (AUS passport) however a guy in my group with a French passport got his 2nd Back-to-Back SETV with the red stamp.
Took the mini-van to the Sadao border. A new processing building has replaced the old "toll gate" style counters and was labled "Temporary System Experiment". I can confirm the 200baht "tip fee" has been replaced with a requirement to show 20K baht cash or foreign equivalent but is randomly asked. With my 4 Back2Back SETV's I was ready to show the 20K cash but I wasn't asked to show anything, a Canadian with 4 SETV's in my group was also not asked as was a Brit with a Working Permit/Business Visa however some other Brits, Russians, French, and Indonesians were asked. One English lady only had 10K cash and was denied entry but no record left in her passport, she borrowed 10K from the Russians, lined up again and went to a different counter, this time she was not asked to show money and got accepted.
There is an interigation room in open view behind the counters, it all just seems completely random as some people with singlets, huge backpacks and scruffy hair were not asked to show anything. The que is ridicoulsy insane as the car park is choc full of Malaysian & Thai Tour Buses and mini vans.
My tip for Tourist Visa entrants going to Sadao: DO NOT roll the dice and come unprepared! Bring 20K cash, you hotel reservation and proof of onward flight because this is obviously random screening and that interrogation room was never empty, it was full of people crying in sorrow or screaming in anger. The rumours in Penang are min 10K that is not true it is 20K! Plenty of sniggering mini van drivers in the car park poaching denied tourists for a ride back to Penang :P
TLDR : Answer Summary
A traveler reports their experience obtaining a back-to-back Single Entry Tourist Visa (SETV) at the Sadao border, highlighting random cash verification where some travelers were asked to show 20,000 baht. Despite having multiple successful crossings, the process appeared inconsistent, with some being asked for cash and others not. Tourists are advised to be prepared with cash, hotel reservations, and proof of onward travel due to the unpredictable nature of entry requirements.