I saw this "information" also. This is Thailand. There are rules and there are "rules". Every "rule" is open to the interpretation of the immigration officer. The more times you come to thailand in a short period of time, the shakier the ground becomes.
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cash. Ticket out. Accommodation booking. Those 3 things all help.
A common misconception. As an airline employee and Visa-checking specialist, I can confirm that the wording in TIMATIC (the reference book used by all airlines) is "passengers without an onward or return ticket may be refused entry".